From 3f583b5a165e7fd11bbb9f38c11020905010e4b7 Mon Sep 17 00:00:00 2001
From: atlowChemi <chemi@atlow.co.il>
Date: Thu, 30 Apr 2026 19:24:30 +0300
Subject: [PATCH] test_runner: extend tag filter with boolean expression DSL

Upgrades the experimental tag filter introduced by stage 1 to accept a
boolean expression instead of a literal tag name.

Grammar: `and`/`&&`, `or`/`||`, `not`/`!`, parentheses for grouping,
and `*` wildcards inside identifiers. Standard precedence
(`not > and > or`); binary operators are left-associative. Word forms
require whitespace separation; punctuation forms do not. Untagged
tests evaluate `false` for any include expression and `true` for
`not X`, so excluding tags does not accidentally remove untagged
tests.

The flag and `testTagFilters` option are still repeatable; multiple
expressions still AND together. Malformed expressions fail fast at
the parent process at startup.

Tag value validation tightens to reject whitespace, operator
characters (`& | ! ( ) *`), and the reserved words `and`/`or`/`not`
in any casing - a breaking change relative to the stage 1 ship,
acceptable at Stability 1.0 (Early development).

Signed-off-by: atlowChemi <chemi@atlow.co.il>
---
 doc/api/cli.md                                |  22 +-
 doc/api/test.md                               |  99 +++-
 doc/node.1                                    |   8 +-
 lib/internal/test_runner/runner.js            |  28 +-
 lib/internal/test_runner/tag_filter.js        | 446 ++++++++++++++++--
 lib/internal/test_runner/utils.js             |  19 +-
 test/parallel/test-runner-tag-filter-cli.mjs  |  81 +++-
 .../test-runner-tag-filter-parser.mjs         | 257 ++++++++++
 test/parallel/test-runner-tags-events.mjs     |   8 +
 .../test-runner-tags-experimental-warning.mjs |   2 +-
 test/parallel/test-runner-tags-validation.mjs |  29 +-
 11 files changed, 905 insertions(+), 94 deletions(-)
 create mode 100644 test/parallel/test-runner-tag-filter-parser.mjs

diff --git a/doc/api/cli.md b/doc/api/cli.md
index 8f7d6185ac464c..b8619da43e7861 100644
--- a/doc/api/cli.md
+++ b/doc/api/cli.md
@@ -1413,7 +1413,7 @@ Enable module mocking in the test runner.
 
 This feature requires `--allow-worker` if used with the [Permission Model][].
 
-### `--experimental-test-tag-filter=<tag>`
+### `--experimental-test-tag-filter='<expr>'`
 
 <!-- YAML
 added: REPLACEME
@@ -1421,14 +1421,20 @@ added: REPLACEME
 
 > Stability: 1.0 - Early development
 
-Run only tests whose tag set contains `<tag>`. Tests declare tags via the
-`tags` option on `test()`, `it()`, `suite()`, or `describe()`; tags
-inherit from suites to nested tests by union. Filtering is
-case-insensitive.
+Run only tests that match the provided boolean tag-filter expression. Tests
+declare tags via the `tags` option on `test()`, `it()`, `suite()`, or
+`describe()`. Tags inherit from suites to nested tests by union.
 
-The flag may be specified more than once; tests must contain **every**
-filter value to run. See [Test tags][] for details on declaring and
-inheriting tags.
+The expression supports boolean operators (`and`/`&&`, `or`/`||`,
+`not`/`!`), parentheses for grouping, and `*` wildcards inside identifiers.
+Standard precedence applies: `not` binds tighter than `and`, which binds
+tighter than `or`. See [Test tags][] for the full grammar and behavior.
+
+The flag may be specified more than once; multiple expressions are combined
+with AND, so a test must satisfy every expression to run.
+
+A malformed expression causes the test runner to exit with a non-zero status
+before running any tests.
 
 ### `--experimental-vm-modules`
 
diff --git a/doc/api/test.md b/doc/api/test.md
index b17c3fd4f6685b..0ffcd46ee83183 100644
--- a/doc/api/test.md
+++ b/doc/api/test.md
@@ -489,8 +489,8 @@ added: REPLACEME
 
 Tags annotate tests and suites with arbitrary string labels. The
 [`--experimental-test-tag-filter`][] CLI flag (or the `testTagFilters`
-option on [`run()`][]) selects tests whose tag set contains every
-provided filter value.
+option on [`run()`][]) selects tests by a boolean expression over those
+labels.
 
 Tags are an alternative to encoding metadata into test names. They are
 useful for cross-cutting axes such as subsystem, speed bucket, flakiness,
@@ -523,37 +523,89 @@ describe('database', { tags: ['db'] }, () => {
 });
 ```
 
-Tag values must be non-empty strings. Tags are matched case-insensitively;
-the canonical form is lowercase. Duplicates within a single `tags` array
-are collapsed on the lowercased form, preserving the first-seen
-declaration order.
+Tag values must be non-empty strings that contain no whitespace, no
+operator characters (`& | ! ( ) *`), and are not the reserved words
+`'and'`, `'or'`, or `'not'` in any casing. Tags are matched
+case-insensitively; the canonical form is lowercase. Duplicates within a
+single `tags` array are collapsed on the lowercased form, preserving the
+first-seen declaration order.
 
 Hooks (`before`, `after`, `beforeEach`, `afterEach`) do not declare their
 own tags. They run as part of their owning suite, which carries the
 suite's tags.
 
-### Filtering by tag
+### Filtering syntax
 
-Each [`--experimental-test-tag-filter`][] value is a literal tag name. A
-test runs only when its tag set contains that name. The flag may be
-specified more than once; tests must match **every** filter to run. The
-same applies to the `testTagFilters` array on [`run()`][]. Filters are
-case-insensitive and AND'd with [`--test-name-pattern`][],
-[`--test-skip-pattern`][], and `.only` filtering.
+The filter expression supports:
 
-Untagged tests are excluded under any non-empty filter, since the filter
-requires the tag to be present.
+* Identifiers—any non-whitespace, non-operator characters. A literal
+  identifier matches a tag of the same value (case-insensitive).
+* `*` wildcards inside an identifier match any sequence of characters.
+  A bare `*` matches any tagged test.
+* Boolean operators with two equivalent forms:
+  * `and` / `&&`
+  * `or` / `||`
+  * `not` / `!`
+* Parentheses for grouping.
 
-### Reading tags from inside a test
+The word forms (`and`, `or`, `not`) require whitespace separation; the
+punctuation forms do not.
+
+#### Operator precedence
+
+The expression is evaluated with the standard precedence
+`not > and > or`. Binary operators are left-associative.
+
+| Expression     | Equivalent grouping |
+| -------------- | ------------------- |
+| `a or b and c` | `a or (b and c)`    |
+| `not a and b`  | `(not a) and b`     |
+
+Use parentheses to override:
+
+| Expression                     | Selects                                    |
+| ------------------------------ | ------------------------------------------ |
+| `(unit or smoke) and not slow` | unit-or-smoke tests that are not also slow |
+| `db && !flaky`                 | db tests that are not flaky                |
+| `*`                            | every tagged test                          |
+
+#### Untagged tests
+
+Untagged tests behave as if they have an empty tag set. As a result:
+
+| Filter expression        | Untagged test | Why                                              |
+| ------------------------ | ------------- | ------------------------------------------------ |
+| `db`                     | excluded      | Positive match against an empty tag set is false |
+| `*`                      | excluded      | The bare wildcard requires at least one tag      |
+| `db or unit`             | excluded      | Both branches are false against an empty tag set |
+| `not flaky`              | included      | Negation against an empty tag set is true        |
+| `not flaky and not slow` | included      | Both negations are true against an empty tag set |
+| `db or not flaky`        | included      | The negated branch is true                       |
+
+For example, `--experimental-test-tag-filter='not flaky'` runs every test
+that is not tagged `flaky`, including all untagged tests.
+
+#### Composing multiple filters
+
+[`--experimental-test-tag-filter`][] may be specified more than once on the
+command line. Multiple expressions compose by AND—a test must satisfy
+every expression to run. The same applies to passing an array to
+`testTagFilters` on [`run()`][]. The tag filter is also AND'd with
+[`--test-name-pattern`][], [`--test-skip-pattern`][], and `.only`
+filtering.
+
+#### Reading tags from inside a test
 
 The [`TestContext`][] object exposes the test's tags as a frozen array
 through [`context.tags`][], so tests can branch on their own metadata.
 
-### Errors
+#### Errors
 
 A tag value that violates the validation rules above throws
 `ERR_INVALID_ARG_VALUE` at the registration site, before any test runs.
-A non-array `tags` value throws `ERR_INVALID_ARG_TYPE`.
+A non-array `tags` value throws `ERR_INVALID_ARG_TYPE`. A malformed
+filter expression on the CLI causes the test runner to exit with a
+non-zero status before running any test files.
 
 ## Extraneous asynchronous activity
 
@@ -826,7 +878,7 @@ test runner functionality:
 
 * `--test` - Prevented to avoid recursive test execution
 * `--experimental-test-coverage` - Managed by the test runner
-* `--experimental-test-tag-filter` - Filter values are validated by the parent
+* `--experimental-test-tag-filter` - Filter expressions are validated by the parent
   process and re-emitted to child processes
 * `--watch` - Watch mode is handled at the parent level
 * `--experimental-default-config-file` - Config file loading is handled by the parent
@@ -1737,10 +1789,11 @@ changes:
     For each test that is executed, any corresponding test hooks, such as
     `beforeEach()`, are also run.
     **Default:** `undefined`.
-  * `testTagFilters` {string|string\[]} A tag name, or an array of tag names,
-    used to filter tests by their declared tags. Tests must contain every
-    listed tag to run. Equivalent to passing [`--experimental-test-tag-filter`][]
-    on the command line. See [Test tags][]. **Default:** `undefined`.
+  * `testTagFilters` {string|string\[]} A boolean expression, or an array of
+    boolean expressions, used to filter tests by their declared tags.
+    Multiple expressions compose by AND. Equivalent to passing
+    [`--experimental-test-tag-filter`][] on the command line. See
+    [Test tags][]. **Default:** `undefined`.
   * `timeout` {number} A number of milliseconds the test execution will
     fail after.
     If unspecified, subtests inherit this value from their parent.
diff --git a/doc/node.1 b/doc/node.1
index e79021eaa666a3..3c52d0fa3b5c36 100644
--- a/doc/node.1
+++ b/doc/node.1
@@ -776,9 +776,11 @@ collecting code coverage from tests for more details.
 Enable module mocking in the test runner.
 This feature requires \fB--allow-worker\fR if used with the Permission Model.
 .
-.It Fl -experimental-test-tag-filter Ar tag
-Run only tests whose tag set contains \fItag\fR. May be specified multiple
-times; tests must contain every filter to run.
+.It Fl -experimental-test-tag-filter Ar expr
+Run only tests that match the boolean tag-filter expression.
+The expression supports \fBand\fR/\fB&&\fR, \fBor\fR/\fB||\fR, \fBnot\fR/\fB!\fR,
+parentheses, and \fB*\fR wildcards. May be specified multiple times; multiple
+expressions are AND'd together.
 .
 .It Fl -experimental-vm-modules
 Enable experimental ES Module support in the \fBnode:vm\fR module.
diff --git a/lib/internal/test_runner/runner.js b/lib/internal/test_runner/runner.js
index 1b0dfb51b21fbe..80b1a81f949856 100644
--- a/lib/internal/test_runner/runner.js
+++ b/lib/internal/test_runner/runner.js
@@ -93,7 +93,7 @@ const {
   parseCommandLine,
 } = require('internal/test_runner/utils');
 const {
-  validateAndCanonicalizeTagFilter,
+  parseTagFilterExpression,
 } = require('internal/test_runner/tag_filter');
 const { Glob } = require('internal/fs/glob');
 const { once } = require('events');
@@ -217,7 +217,7 @@ function getRunArgs(path, { forceExit,
     ArrayPrototypeForEach(testSkipPatterns, (pattern) => ArrayPrototypePush(runArgs, `--test-skip-pattern=${pattern}`));
   }
   if (testTagFilterExpressions != null) {
-    ArrayPrototypeForEach(testTagFilterExpressions, (value) => ArrayPrototypePush(runArgs, `--experimental-test-tag-filter=${value}`));
+    ArrayPrototypeForEach(testTagFilterExpressions, (expr) => ArrayPrototypePush(runArgs, `--experimental-test-tag-filter=${expr}`));
   }
   if (only === true) {
     ArrayPrototypePush(runArgs, '--test-only');
@@ -809,6 +809,14 @@ function run(options = kEmptyObject) {
     });
   }
 
+  // The public contract of testTagFilters is `string | string[]`. The
+  // parseCommandLine bootstrap path piggybacks the already-parsed AST array
+  // on the same field, identifiable by the sibling testTagFilterExpressions
+  // field which only that path sets. When that marker is present and the
+  // first element isn't a string, treat the array as ASTs and skip the
+  // public validation loop. Otherwise validate every element as a string,
+  // so any non-string input throws ERR_INVALID_ARG_TYPE with the offending
+  // index regardless of position.
   let testTagFilterExpressions = null;
   if (testTagFilters != null) {
     if (!ArrayIsArray(testTagFilters)) {
@@ -816,12 +824,19 @@ function run(options = kEmptyObject) {
     }
     if (testTagFilters.length === 0) {
       testTagFilters = null;
+    } else if (options.testTagFilterExpressions != null &&
+               typeof testTagFilters[0] !== 'string') {
+      // Internal bootstrap: trust the AST array as already-parsed.
     } else {
       emitExperimentalWarning('Test tags');
-      testTagFilters = ArrayPrototypeMap(testTagFilters, (value, i) => (
-        validateAndCanonicalizeTagFilter(value, `options.testTagFilters[${i}]`)
-      ));
-      testTagFilterExpressions = testTagFilters;
+      testTagFilterExpressions = ArrayPrototypeSlice(testTagFilters);
+      testTagFilters = ArrayPrototypeMap(testTagFilters, (value, i) => {
+        const name = `options.testTagFilters[${i}]`;
+        if (typeof value !== 'string') {
+          throw new ERR_INVALID_ARG_TYPE(name, 'string', value);
+        }
+        return parseTagFilterExpression(value, name);
+      });
     }
   }
   testTagFilterExpressions ??= options.testTagFilterExpressions;
@@ -922,7 +937,6 @@ function run(options = kEmptyObject) {
     inspectPort,
     testNamePatterns,
     testSkipPatterns,
-    testTagFilters,
     testTagFilterExpressions,
     hasFiles: files != null,
     globPatterns,
diff --git a/lib/internal/test_runner/tag_filter.js b/lib/internal/test_runner/tag_filter.js
index 35dc2647a2aac0..0151abf31cc738 100644
--- a/lib/internal/test_runner/tag_filter.js
+++ b/lib/internal/test_runner/tag_filter.js
@@ -2,8 +2,14 @@
 const {
   ArrayPrototypePush,
   ObjectFreeze,
+  RegExp,
+  RegExpPrototypeExec,
   SafeSet,
+  StringPrototypeCharCodeAt,
+  StringPrototypeSlice,
+  StringPrototypeSplit,
   StringPrototypeToLowerCase,
+  StringPrototypeTrim,
 } = primordials;
 
 const {
@@ -19,14 +25,68 @@ const {
   validateString,
 } = require('internal/validators');
 
+const kCharAmpersand = 0x26;
+const kCharBackslash = 0x5C;
+const kCharCarriageReturn = 0x0D;
+const kCharCaret = 0x5E;
+const kCharDollar = 0x24;
+const kCharDot = 0x2E;
+const kCharExclaim = 0x21;
+const kCharFormFeed = 0x0C;
+const kCharLBrace = 0x7B;
+const kCharLBracket = 0x5B;
+const kCharLineFeed = 0x0A;
+const kCharLParen = 0x28;
+const kCharPipe = 0x7C;
+const kCharPlus = 0x2B;
+const kCharQuestion = 0x3F;
+const kCharRBrace = 0x7D;
+const kCharRBracket = 0x5D;
+const kCharRParen = 0x29;
+const kCharSpace = 0x20;
+const kCharStar = 0x2A;
+const kCharTab = 0x09;
+const kCharVerticalTab = 0x0B;
+
+// Single `&` and `|` are allowed here: standalone they have no operator
+// meaning, only the doubled forms `&&` and `||` do.
+const kTagForbiddenChars = new SafeSet([
+  kCharTab, kCharLineFeed, kCharVerticalTab, kCharFormFeed, kCharCarriageReturn, kCharSpace,
+  kCharAmpersand, kCharExclaim, kCharLParen, kCharPipe, kCharRParen, kCharStar,
+]);
+
+const kReservedWords = new SafeSet(['and', 'or', 'not']);
+
+/**
+ * Frozen, shared empty array used as the canonical "no tags" value for
+ * tests that don't declare their own and have no tagged ancestors.
+ * Sharing one frozen instance avoids per-test allocation.
+ * @type {readonly string[]}
+ */
 const kEmptyTagArray = ObjectFreeze([]);
 
+function isWhitespace(ch) {
+  return ch === kCharTab || ch === kCharLineFeed || ch === kCharVerticalTab ||
+         ch === kCharFormFeed || ch === kCharCarriageReturn || ch === kCharSpace;
+}
+
+// `*` is intentionally not a break char: it's allowed inside an identifier
+// and becomes a wildcard.
+function isIdentBreak(ch) {
+  return isWhitespace(ch) ||
+         ch === kCharAmpersand || ch === kCharPipe ||
+         ch === kCharExclaim || ch === kCharLParen || ch === kCharRParen;
+}
+
 /**
  * Validate and canonicalize a `tags` option value supplied to `test()`,
  * `it()`, `suite()`, or `describe()`.
  *
- * Each tag must be a non-empty string. Tags are canonicalized to lowercase
- * and deduplicated, preserving first-seen declaration order.
+ * Each tag must be a non-empty string that contains no whitespace, no
+ * operator characters (`& | ! ( ) *`), and is not the reserved word
+ * `'and'`, `'or'`, or `'not'` in any casing. Tags are canonicalized to
+ * lowercase and deduplicated on the lowercased form, preserving the
+ * first-seen declaration order.
  *
  * Calling this with a non-empty array also emits the one-shot
  * `ExperimentalWarning` for the test-tags feature.
@@ -37,7 +97,8 @@ const kEmptyTagArray = ObjectFreeze([]);
  *   Returns an empty array when `tags` is `[]`.
  * @throws {ERR_INVALID_ARG_TYPE} If `tags` is not an array, or any element
  *   is not a string.
- * @throws {ERR_INVALID_ARG_VALUE} If any element is empty.
+ * @throws {ERR_INVALID_ARG_VALUE} If any element is empty, contains a
+ *   forbidden character, or is a reserved word in any casing.
  */
 function validateAndCanonicalizeTagValues(tags, optName) {
   validateArray(tags, optName);
@@ -55,7 +116,34 @@ function validateAndCanonicalizeTagValues(tags, optName) {
     const tag = tags[i];
     const elemName = `${optName}[${i}]`;
 
-    const lower = validateAndCanonicalizeTagFilter(tag, elemName);
+    validateString(tag, elemName);
+
+    if (tag.length === 0) {
+      throw new ERR_INVALID_ARG_VALUE(elemName, tag, 'must not be empty');
+    }
+
+    for (let j = 0; j < tag.length; j++) {
+      const ch = StringPrototypeCharCodeAt(tag, j);
+      if (kTagForbiddenChars.has(ch)) {
+        throw new ERR_INVALID_ARG_VALUE(
+          elemName,
+          tag,
+          'contains a forbidden character. Tags must not contain whitespace, ' +
+          'operator characters (&, |, !, (, ), *), or be the reserved words ' +
+          '\'and\', \'or\', or \'not\'',
+        );
+      }
+    }
+
+    const lower = StringPrototypeToLowerCase(tag);
+
+    if (kReservedWords.has(lower)) {
+      throw new ERR_INVALID_ARG_VALUE(
+        elemName,
+        tag,
+        'must not be the reserved word \'and\', \'or\', or \'not\'',
+      );
+    }
 
     if (!seen.has(lower)) {
       seen.add(lower);
@@ -66,43 +154,341 @@ function validateAndCanonicalizeTagValues(tags, optName) {
   return ObjectFreeze(result);
 }
 
+// ---------------------------------------------------------------------------
+// Lexer
+// ---------------------------------------------------------------------------
+
+// Token types
+const T_AND = 'AND';
+const T_OR = 'OR';
+const T_NOT = 'NOT';
+const T_LPAREN = 'LPAREN';
+const T_RPAREN = 'RPAREN';
+const T_IDENT = 'IDENT';
+const T_EOF = 'EOF';
+
+function lex(expr, name) {
+  const tokens = [];
+  let i = 0;
+  const len = expr.length;
+
+  while (i < len) {
+    const ch = StringPrototypeCharCodeAt(expr, i);
+
+    if (isWhitespace(ch)) {
+      i++;
+      continue;
+    }
+
+    if (ch === kCharAmpersand) {
+      if (i + 1 < len && StringPrototypeCharCodeAt(expr, i + 1) === kCharAmpersand) {
+        ArrayPrototypePush(tokens, { __proto__: null, type: T_AND, pos: i });
+        i += 2;
+      } else {
+        throw new ERR_INVALID_ARG_VALUE(
+          name, expr,
+          `unexpected '&' at position ${i}; use '&&' or 'and'`,
+        );
+      }
+      continue;
+    }
+
+    if (ch === kCharPipe) {
+      if (i + 1 < len && StringPrototypeCharCodeAt(expr, i + 1) === kCharPipe) {
+        ArrayPrototypePush(tokens, { __proto__: null, type: T_OR, pos: i });
+        i += 2;
+      } else {
+        throw new ERR_INVALID_ARG_VALUE(
+          name, expr,
+          `unexpected '|' at position ${i}; use '||' or 'or'`,
+        );
+      }
+      continue;
+    }
+
+    if (ch === kCharExclaim) {
+      ArrayPrototypePush(tokens, { __proto__: null, type: T_NOT, pos: i });
+      i++;
+      continue;
+    }
+
+    if (ch === kCharLParen) {
+      ArrayPrototypePush(tokens, { __proto__: null, type: T_LPAREN, pos: i });
+      i++;
+      continue;
+    }
+
+    if (ch === kCharRParen) {
+      ArrayPrototypePush(tokens, { __proto__: null, type: T_RPAREN, pos: i });
+      i++;
+      continue;
+    }
+
+    const start = i;
+    while (i < len && !isIdentBreak(StringPrototypeCharCodeAt(expr, i))) {
+      i++;
+    }
+    const ident = StringPrototypeSlice(expr, start, i);
+    const lower = StringPrototypeToLowerCase(ident);
+
+    if (lower === 'and') {
+      ArrayPrototypePush(tokens, { __proto__: null, type: T_AND, pos: start });
+    } else if (lower === 'or') {
+      ArrayPrototypePush(tokens, { __proto__: null, type: T_OR, pos: start });
+    } else if (lower === 'not') {
+      ArrayPrototypePush(tokens, { __proto__: null, type: T_NOT, pos: start });
+    } else {
+      ArrayPrototypePush(tokens, { __proto__: null, type: T_IDENT, value: ident, pos: start });
+    }
+  }
+
+  ArrayPrototypePush(tokens, { __proto__: null, type: T_EOF, pos: len });
+  return tokens;
+}
+
+// ---------------------------------------------------------------------------
+// Regex escaping for wildcard tags
+// ---------------------------------------------------------------------------
+
+// `*` is the only metacharacter intentionally not escaped: the caller
+// handles it as a wildcard.
+function escapeForRegExp(str) {
+  let result = '';
+  for (let i = 0; i < str.length; i++) {
+    const ch = StringPrototypeCharCodeAt(str, i);
+    if (
+      ch === kCharLBracket || ch === kCharRBracket ||
+      ch === kCharLParen || ch === kCharRParen ||
+      ch === kCharLBrace || ch === kCharRBrace ||
+      ch === kCharCaret || ch === kCharDollar ||
+      ch === kCharDot || ch === kCharPlus ||
+      ch === kCharQuestion || ch === kCharBackslash ||
+      ch === kCharPipe
+    ) {
+      result += '\\';
+    }
+    result += StringPrototypeSlice(str, i, i + 1);
+  }
+  return result;
+}
+
+function buildWildcardRegex(ident) {
+  // Lowercase the source first and drop the /i flag, so wildcard matching
+  // uses the same casing semantics as literal matching (which lowercases the
+  // tag value at validation time). Using /i would diverge for non-ASCII
+  // characters whose String.prototype.toLowerCase() output differs from
+  // RegExp /i case folding (e.g. Turkish I-with-dot U+0130).
+  const parts = StringPrototypeSplit(StringPrototypeToLowerCase(ident), '*');
+  let pattern = '^';
+  for (let i = 0; i < parts.length; i++) {
+    if (i > 0) {
+      pattern += '.*';
+    }
+    pattern += escapeForRegExp(parts[i]);
+  }
+  pattern += '$';
+  return new RegExp(pattern);
+}
+
+function makeTagNode(ident) {
+  for (let i = 0; i < ident.length; i++) {
+    if (StringPrototypeCharCodeAt(ident, i) === kCharStar) {
+      return { __proto__: null, type: 'wildcard', re: buildWildcardRegex(ident) };
+    }
+  }
+  return { __proto__: null, type: 'tag', value: StringPrototypeToLowerCase(ident) };
+}
+
+// ---------------------------------------------------------------------------
+// Parser - recursive descent
+// Precedence: not > and > or  (standard Boolean)
+// ---------------------------------------------------------------------------
+
 /**
- * Validate and canonicalize a single tag-filter string supplied via
- * `--experimental-test-tag-filter` or `testTagFilters`.
+ * Parse a tag filter expression string into an AST suitable for
+ * `evaluateTagFilters`.
  *
- * Filters are literal tag names: a test passes the filter when its tag set
- * contains the lowercased filter value. Multi-occurrence composes by AND
- * at the call site (see `evaluateTagFilters`).
- * @param {unknown} value - The supplied filter string.
- * @param {string} name - Argument name embedded in thrown error messages.
- * @returns {string} The lowercased filter value.
- * @throws {ERR_INVALID_ARG_TYPE} If `value` is not a string.
- * @throws {ERR_INVALID_ARG_VALUE} If `value` is empty.
+ * Supported syntax:
+ *   - Identifiers: any non-whitespace, non-operator characters; case-
+ *     insensitive when matched. A `*` inside an identifier becomes a
+ *     wildcard that matches any sequence of characters; a bare `*`
+ *     matches any non-empty tag.
+ *   - Boolean operators: `and`/`&&`, `or`/`||`, `not`/`!`, with the
+ *     standard precedence `not > and > or` and left-associative binary
+ *     operators. Word forms must be whitespace-separated; punctuation
+ *     forms do not.
+ *   - Parentheses for grouping.
+ * @param {string} expr - The expression to parse.
+ * @param {string} name - Option name to embed in thrown error messages
+ *   (typically `'--experimental-test-tag-filter[<i>]'` or
+ *   `'options.testTagFilters[<i>]'`).
+ * @returns {object} An opaque AST node. The shape is internal; pass it
+ *   only to `evaluateTagFilters`.
+ * @throws {ERR_INVALID_ARG_TYPE} If `expr` is not a string.
+ * @throws {ERR_INVALID_ARG_VALUE} If `expr` is empty, contains only
+ *   whitespace, or has a syntax error (unbalanced parentheses, dangling
+ *   operator, adjacent identifiers, etc.). The error message includes
+ *   the offending position.
  */
-function validateAndCanonicalizeTagFilter(value, name) {
-  validateString(value, name);
+function parseTagFilterExpression(expr, name) {
+  validateString(expr, name);
+
+  if (StringPrototypeTrim(expr).length === 0) {
+    throw new ERR_INVALID_ARG_VALUE(name, expr, 'must not be empty');
+  }
+
+  const tokens = lex(expr, name);
+  let pos = 0;
+
+  function peek() {
+    return tokens[pos];
+  }
+
+  function consume() {
+    return tokens[pos++];
+  }
+
+  function parseExpr() {
+    return parseOr();
+  }
+
+  function parseOr() {
+    let left = parseAnd();
+    while (peek().type === T_OR) {
+      consume();
+      const right = parseAnd();
+      left = { __proto__: null, type: 'or', left, right };
+    }
+    return left;
+  }
 
-  if (value.length === 0) {
-    throw new ERR_INVALID_ARG_VALUE(name, value, 'must not be empty');
+  function parseAnd() {
+    let left = parseNot();
+    while (peek().type === T_AND) {
+      consume();
+      const right = parseNot();
+      left = { __proto__: null, type: 'and', left, right };
+    }
+    return left;
   }
 
-  return StringPrototypeToLowerCase(value);
+  function parseNot() {
+    if (peek().type === T_NOT) {
+      const { pos: notPos } = consume();
+      if (peek().type === T_EOF) {
+        throw new ERR_INVALID_ARG_VALUE(
+          name, expr,
+          `expected operand after 'not' at position ${notPos}`,
+        );
+      }
+      const operand = parseNot();
+      return { __proto__: null, type: 'not', operand };
+    }
+
+    if (peek().type === T_LPAREN) {
+      const { pos: lPos } = consume();
+      if (peek().type === T_EOF) {
+        throw new ERR_INVALID_ARG_VALUE(
+          name, expr,
+          `unmatched '(' at position ${lPos}`,
+        );
+      }
+      const inner = parseExpr();
+      if (peek().type !== T_RPAREN) {
+        throw new ERR_INVALID_ARG_VALUE(
+          name, expr,
+          `expected ')' at position ${peek().pos}`,
+        );
+      }
+      consume();
+      return inner;
+    }
+
+    if (peek().type === T_IDENT) {
+      const { value } = consume();
+      return makeTagNode(value);
+    }
+
+    const tok = peek();
+    throw new ERR_INVALID_ARG_VALUE(
+      name, expr,
+      `unexpected token '${tok.type}' at position ${tok.pos}`,
+    );
+  }
+
+  const ast = parseExpr();
+
+  if (peek().type !== T_EOF) {
+    const tok = peek();
+    throw new ERR_INVALID_ARG_VALUE(
+      name, expr,
+      `unexpected token at position ${tok.pos}`,
+    );
+  }
+
+  return ast;
 }
 
+// ---------------------------------------------------------------------------
+// Evaluator
+// ---------------------------------------------------------------------------
+
 /**
- * Evaluate a list of tag filters against a test's tag set.
+ * Evaluate a tag filter AST against a set of test tags.
+ *
+ * Untagged tests have an empty SafeSet. The semantics are:
+ *   - An include expression (tag/wildcard/and/or) evaluates false for empty set.
+ *   - 'not X' evaluates true when X is false (so untagged tests pass 'not X').
+ * @param {object} ast - AST node from parseTagFilterExpression.
+ * @param {SafeSet} tags - Lowercased canonical tags for the test.
+ * @returns {boolean}
+ */
+function evaluateTagFilter(ast, tags) {
+  const { type } = ast;
+
+  if (type === 'or') {
+    return evaluateTagFilter(ast.left, tags) || evaluateTagFilter(ast.right, tags);
+  }
+
+  if (type === 'and') {
+    return evaluateTagFilter(ast.left, tags) && evaluateTagFilter(ast.right, tags);
+  }
+
+  if (type === 'not') {
+    return !evaluateTagFilter(ast.operand, tags);
+  }
+
+  if (type === 'tag') {
+    return tags.has(ast.value);
+  }
+
+  // type === 'wildcard'
+  let matched = false;
+  tags.forEach((tag) => {
+    if (!matched && RegExpPrototypeExec(ast.re, tag) !== null) {
+      matched = true;
+    }
+  });
+  return matched;
+}
+
+/**
+ * Evaluate one or more tag filter ASTs against a test's tag set.
+ *
+ * Multiple ASTs compose by AND: a test passes only when every AST
+ * evaluates true for it. An empty `asts` array always passes.
  *
- * Multiple filters compose by AND: a test passes only when every filter is
- * present in its tag set. An empty `filters` array always passes. Untagged
- * tests have an empty tag set and so are excluded under any non-empty
- * filter.
- * @param {string[]} filters - Lowercased canonical filter values.
- * @param {SafeSet<string>} tags - The test's lowercased canonical tag set.
+ * Untagged tests (an empty `tags` set) fail any include expression
+ * (`tag`, `wildcard`, `and`, `or`) and pass `not X`, so excluding tags
+ * does not accidentally remove untagged tests.
+ * @param {object[]} asts - ASTs returned by `parseTagFilterExpression`.
+ * @param {SafeSet<string>} tags - The test's lowercased canonical tag
+ *   set (use `Set` in non-internal contexts; both work).
  * @returns {boolean} `true` if the test should run.
  */
-function evaluateTagFilters(filters, tags) {
-  for (let i = 0; i < filters.length; i++) {
-    if (!tags.has(filters[i])) {
+function evaluateTagFilters(asts, tags) {
+  for (let i = 0; i < asts.length; i++) {
+    if (!evaluateTagFilter(asts[i], tags)) {
       return false;
     }
   }
@@ -112,6 +498,6 @@ function evaluateTagFilters(filters, tags) {
 module.exports = {
   evaluateTagFilters,
   kEmptyTagArray,
-  validateAndCanonicalizeTagFilter,
+  parseTagFilterExpression,
   validateAndCanonicalizeTagValues,
 };
diff --git a/lib/internal/test_runner/utils.js b/lib/internal/test_runner/utils.js
index 5a29673279311b..f9f8eaa4ac5c4b 100644
--- a/lib/internal/test_runner/utils.js
+++ b/lib/internal/test_runner/utils.js
@@ -31,7 +31,7 @@ const {
 } = primordials;
 
 const {
-  validateAndCanonicalizeTagFilter,
+  parseTagFilterExpression,
 } = require('internal/test_runner/tag_filter');
 
 const { AsyncResource } = require('async_hooks');
@@ -335,17 +335,16 @@ function parseCommandLine() {
     if (tagFilterFlag?.length > 0) {
       emitExperimentalWarning('Test tags');
       testTagFilterExpressions = tagFilterFlag;
-      // Validate at parent startup so a malformed flag fails fast,
-      // independent of isolation mode. Under isolation='process' the
-      // validated strings go unused at the parent (children re-validate
-      // and apply the filter); the validation here only surfaces input
-      // errors early.
-      const validated = ArrayPrototypeMap(
+      // Parse every expression at parent startup so a malformed flag fails
+      // fast, independent of isolation mode. Under isolation='process' the
+      // parsed ASTs go unused (children re-parse and apply the filter), but
+      // running the parser surfaces syntax errors at the parent.
+      const parsed = ArrayPrototypeMap(
         tagFilterFlag,
-        (value, i) => validateAndCanonicalizeTagFilter(value, `--experimental-test-tag-filter[${i}]`),
+        (expr, i) => parseTagFilterExpression(expr, `--experimental-test-tag-filter[${i}]`),
       );
       if (isolation === 'none') {
-        testTagFilters = validated;
+        testTagFilters = parsed;
       }
     }
 
@@ -393,7 +392,7 @@ function parseCommandLine() {
       testTagFilterExpressions = tagFilterFlag;
       testTagFilters = ArrayPrototypeMap(
         tagFilterFlag,
-        (value, i) => validateAndCanonicalizeTagFilter(value, `--experimental-test-tag-filter[${i}]`),
+        (expr, i) => parseTagFilterExpression(expr, `--experimental-test-tag-filter[${i}]`),
       );
     }
   }
diff --git a/test/parallel/test-runner-tag-filter-cli.mjs b/test/parallel/test-runner-tag-filter-cli.mjs
index 13717d34b3edb9..e7a1cd2d1d5ffe 100644
--- a/test/parallel/test-runner-tag-filter-cli.mjs
+++ b/test/parallel/test-runner-tag-filter-cli.mjs
@@ -62,32 +62,55 @@ test('untagged parent runs only the matching tagged child', () => {
   assert.doesNotMatch(stdout, /plain sibling/);
 });
 
+test('not X also includes untagged tests', () => {
+  const { status, stdout } = run(['--experimental-test-tag-filter=not flaky']);
+  assert.strictEqual(status, 0);
+  pass(stdout, 8);
+  assert.match(stdout, /ok \d+ - untagged/);
+  assert.doesNotMatch(stdout, /db flaky/);
+  assert.doesNotMatch(stdout, /^ok \d+ - only flaky/m);
+});
+
 test('repeated --experimental-test-tag-filter ANDs together', () => {
-  // db AND integration: only "db plus integration" satisfies both.
   const { status, stdout } = run([
     '--experimental-test-tag-filter=db',
-    '--experimental-test-tag-filter=integration',
+    '--experimental-test-tag-filter=not flaky',
   ]);
   assert.strictEqual(status, 0);
-  pass(stdout, 1);
+  pass(stdout, 2);
+  assert.match(stdout, /ok \d+ - db only/);
   assert.match(stdout, /ok \d+ - db plus integration/);
-  assert.doesNotMatch(stdout, /^ok \d+ - db only/m);
-  assert.doesNotMatch(stdout, /^ok \d+ - db flaky/m);
+  assert.doesNotMatch(stdout, /db flaky/);
 });
 
-test('untagged tests are excluded under any positive filter', () => {
-  const { status, stdout } = run(['--experimental-test-tag-filter=db']);
+test('bare * matches any tagged test, excludes untagged', () => {
+  const { status, stdout } = run(['--experimental-test-tag-filter=*']);
   assert.strictEqual(status, 0);
+  pass(stdout, 8);
   assert.doesNotMatch(stdout, /^ok \d+ - untagged/m);
 });
 
+test('wildcard prefix: db* matches db, db:postgres, etc.', () => {
+  const { status, stdout } = run(['--experimental-test-tag-filter=db*']);
+  assert.strictEqual(status, 0);
+  pass(stdout, 4);
+  assert.match(stdout, /db wildcard match/);
+});
+
+test('boolean composition: unit && !slow', () => {
+  const { status, stdout } = run(['--experimental-test-tag-filter=unit && !slow']);
+  assert.strictEqual(status, 0);
+  pass(stdout, 1);
+  assert.match(stdout, /ok \d+ - unit only/);
+});
+
 test('isolation=none produces identical filtered set', () => {
-  const proc = run(['--experimental-test-tag-filter=db']);
-  const none = run(['--experimental-test-tag-filter=db'], ['--test-isolation=none']);
+  const proc = run(['--experimental-test-tag-filter=unit && !slow']);
+  const none = run(['--experimental-test-tag-filter=unit && !slow'], ['--test-isolation=none']);
   assert.strictEqual(proc.status, 0);
   assert.strictEqual(none.status, 0);
-  pass(proc.stdout, 3);
-  pass(none.stdout, 3);
+  pass(proc.stdout, 1);
+  pass(none.stdout, 1);
 });
 
 test('combined with --test-skip-pattern (pure AND)', () => {
@@ -101,8 +124,44 @@ test('combined with --test-skip-pattern (pure AND)', () => {
   assert.doesNotMatch(stdout, /db flaky/);
 });
 
+test('malformed expression: unbalanced parenthesis errors at startup', () => {
+  const { status, stderr, stdout } = run(['--experimental-test-tag-filter=(a']);
+  assert.notStrictEqual(status, 0);
+  // Match the full sentinel error line so noise elsewhere in stderr can't
+  // satisfy the assertion via interleaved substrings.
+  assert.match(
+    stderr,
+    /^TypeError \[ERR_INVALID_ARG_VALUE\]: The argument '--experimental-test-tag-filter\[0\]' expected '\)' at position \d+/m,
+  );
+  // No file should have been spawned.
+  assert.doesNotMatch(stdout, /^ok 1 -/m);
+});
+
+test('malformed expression: dangling operator errors at startup', () => {
+  const { status, stderr } = run(['--experimental-test-tag-filter=a and']);
+  assert.notStrictEqual(status, 0);
+  assert.match(
+    stderr,
+    /^TypeError \[ERR_INVALID_ARG_VALUE\]: The argument '--experimental-test-tag-filter\[0\]' unexpected token 'EOF' at position \d+/m,
+  );
+});
+
 test('empty --experimental-test-tag-filter= is rejected by argv parser', () => {
   const { status, stderr } = run(['--experimental-test-tag-filter=']);
   assert.notStrictEqual(status, 0);
   assert.match(stderr, /requires an argument/);
 });
+
+test('reserved word as tag value errors at registration', () => {
+  const child = spawnSync(process.execPath, [
+    '-e',
+    "require('node:test').test('x', { tags: ['and'] }, () => {});",
+  ]);
+  assert.notStrictEqual(child.status, 0);
+  // Match the full sentinel error line so noise elsewhere in stderr can't
+  // satisfy the assertion via interleaved substrings.
+  assert.match(
+    child.stderr.toString(),
+    /^TypeError \[ERR_INVALID_ARG_VALUE\]: The property 'options\.tags\[0\]' must not be the reserved word/m,
+  );
+});
diff --git a/test/parallel/test-runner-tag-filter-parser.mjs b/test/parallel/test-runner-tag-filter-parser.mjs
new file mode 100644
index 00000000000000..0a9ab93dc98cec
--- /dev/null
+++ b/test/parallel/test-runner-tag-filter-parser.mjs
@@ -0,0 +1,257 @@
+// Flags: --expose-internals
+
+import '../common/index.mjs';
+import assert from 'node:assert';
+import { test } from 'node:test';
+import tagFilter from 'internal/test_runner/tag_filter';
+
+const { evaluateTagFilters, parseTagFilterExpression } = tagFilter;
+
+function tagSet(...tags) {
+  return new Set(tags);
+}
+
+function matches(expr, ...tags) {
+  return evaluateTagFilters([parseTagFilterExpression(expr, 'expr')], tagSet(...tags));
+}
+
+test('single identifier', () => {
+  assert.strictEqual(matches('db', 'db'), true);
+  assert.strictEqual(matches('db', 'other'), false);
+  assert.strictEqual(matches('db'), false);
+});
+
+test('case-insensitive match', () => {
+  // The evaluator expects an already-lowercased tag set, so 'DB' in the set
+  // must not match 'db' in the filter.
+  assert.strictEqual(matches('DB', 'db'), true);
+  assert.strictEqual(matches('db', 'DB'), false);
+});
+
+test('and / && have higher precedence than or / ||', () => {
+  for (const expr of ['a or b and c', 'a || b && c']) {
+    assert.strictEqual(matches(expr, 'a'), true);
+    assert.strictEqual(matches(expr, 'b'), false);
+    assert.strictEqual(matches(expr, 'c'), false);
+    assert.strictEqual(matches(expr, 'a', 'b'), true);
+    assert.strictEqual(matches(expr, 'a', 'c'), true);
+    assert.strictEqual(matches(expr, 'b', 'c'), true);
+    assert.strictEqual(matches(expr, 'a', 'b', 'c'), true);
+  }
+});
+
+test('not has higher precedence than and', () => {
+  for (const expr of ['not a and b', '!a && b']) {
+    assert.strictEqual(matches(expr, 'b'), true);
+    assert.strictEqual(matches(expr, 'a', 'b'), false);
+  }
+});
+
+test('not has higher precedence than or', () => {
+  for (const expr of ['not a or b', '!a || b']) {
+    assert.strictEqual(matches(expr), true);
+    assert.strictEqual(matches(expr, 'a'), false);
+    assert.strictEqual(matches(expr, 'b'), true);
+    assert.strictEqual(matches(expr, 'a', 'b'), true);
+  }
+});
+
+test('parentheses override precedence', () => {
+  for (const expr of ['(a or b) and c', '(a || b) && c']) {
+    assert.strictEqual(matches(expr, 'a'), false);
+    assert.strictEqual(matches(expr, 'c'), false);
+    assert.strictEqual(matches(expr, 'a', 'c'), true);
+    assert.strictEqual(matches(expr, 'b', 'c'), true);
+  }
+});
+
+test('double negation', () => {
+  for (const expr of ['not not a', '!!a']) {
+    assert.strictEqual(matches(expr, 'a'), true);
+    assert.strictEqual(matches(expr), false);
+  }
+});
+
+test('mixing word and punctuation forms in one expression', () => {
+  for (const expr of ['unit && not flaky', 'unit and !flaky']) {
+    assert.strictEqual(matches(expr, 'unit'), true);
+    assert.strictEqual(matches(expr, 'unit', 'flaky'), false);
+  }
+});
+
+test('mixed forms inside parentheses, word and punct equivalence', () => {
+  // Each pair below is the same expression in word form and punctuation form.
+  for (const expr of ['a and (b || not c)', 'a && (b or not c)']) {
+    assert.strictEqual(matches(expr, 'a'), true);
+    assert.strictEqual(matches(expr, 'a', 'b'), true);
+    assert.strictEqual(matches(expr, 'a', 'c'), false);
+    assert.strictEqual(matches(expr, 'a', 'b', 'c'), true);
+    assert.strictEqual(matches(expr, 'b'), false);
+  }
+
+  for (const expr of ['(a || b) && !c', '(a or b) and not c']) {
+    assert.strictEqual(matches(expr, 'a'), true);
+    assert.strictEqual(matches(expr, 'b'), true);
+    assert.strictEqual(matches(expr, 'a', 'c'), false);
+    assert.strictEqual(matches(expr, 'c'), false);
+  }
+
+  for (const expr of ['not (a or b) and c', '!(a || b) && c']) {
+    assert.strictEqual(matches(expr, 'c'), true);
+    assert.strictEqual(matches(expr, 'a', 'c'), false);
+    assert.strictEqual(matches(expr, 'b', 'c'), false);
+  }
+
+  for (const expr of ['!(a && b) || c', 'not (a and b) or c']) {
+    assert.strictEqual(matches(expr, 'a'), true);
+    assert.strictEqual(matches(expr, 'a', 'b'), false);
+    assert.strictEqual(matches(expr, 'a', 'b', 'c'), true);
+  }
+});
+
+test('nested parentheses and wildcards mixed with word forms', () => {
+  for (const expr of [
+    '(db* or unit) and not (slow || flaky)',
+    '(db* || unit) && !(slow or flaky)',
+  ]) {
+    assert.strictEqual(matches(expr, 'db'), true);
+    assert.strictEqual(matches(expr, 'db:postgres'), true);
+    assert.strictEqual(matches(expr, 'unit'), true);
+    assert.strictEqual(matches(expr, 'unit', 'slow'), false);
+    assert.strictEqual(matches(expr, 'db', 'flaky'), false);
+    assert.strictEqual(matches(expr, 'mongo'), false);
+  }
+});
+
+test("'notslow' is one identifier, 'not slow' is two tokens", () => {
+  assert.strictEqual(matches('notslow', 'notslow'), true);
+  assert.strictEqual(matches('notslow', 'slow'), false);
+  assert.strictEqual(matches('not slow'), true);
+  assert.strictEqual(matches('not slow', 'slow'), false);
+});
+
+test('punctuation does not need whitespace separation', () => {
+  assert.strictEqual(matches('!a', 'b'), true);
+  assert.strictEqual(matches('!a', 'a'), false);
+  assert.strictEqual(matches('a&&b', 'a', 'b'), true);
+  assert.strictEqual(matches('a||b', 'a'), true);
+});
+
+test('wildcard expands across allowed alphabet', () => {
+  assert.strictEqual(matches('db*', 'db'), true);
+  assert.strictEqual(matches('db*', 'db1'), true);
+  assert.strictEqual(matches('db*', 'db:postgres'), true);
+  assert.strictEqual(matches('db*', 'mongo'), false);
+});
+
+test('bare * matches any tagged test', () => {
+  assert.strictEqual(matches('*', 'anything'), true);
+  assert.strictEqual(matches('*', 'a', 'b'), true);
+  assert.strictEqual(matches('*'), false);
+});
+
+test('wildcard in middle and at start', () => {
+  assert.strictEqual(matches('*db', 'mydb'), true);
+  assert.strictEqual(matches('*db', 'db'), true);
+  assert.strictEqual(matches('*db', 'dbmy'), false);
+  assert.strictEqual(matches('a*z', 'abz'), true);
+  assert.strictEqual(matches('a*z', 'az'), true);
+  assert.strictEqual(matches('a*z', 'abc'), false);
+});
+
+test('regex metacharacters in tags are escaped', () => {
+  // The literal `.` in the filter must match a literal dot only, not any
+  // arbitrary character (which would be the unescaped regex meaning).
+  assert.strictEqual(matches('a.b*', 'a.b'), true);
+  assert.strictEqual(matches('a.b*', 'axb'), false);
+});
+
+test('wildcard case-folding matches literal-tag case-folding for non-ASCII', () => {
+  // Authoring a tag 'İ' (U+0130) goes through String.prototype.toLowerCase
+  // and stores 'i̇' (two code points). Wildcard matching must use the same
+  // fold so authors see consistent behavior across literal and wildcard
+  // filters.
+  const folded = 'İ'.toLowerCase();
+  assert.strictEqual(matches('İ', folded), true);
+  assert.strictEqual(matches('İ*', folded), true);
+  assert.strictEqual(matches('İ*', `${folded}foo`), true);
+  assert.strictEqual(matches('*İ', `foo${folded}`), true);
+});
+
+test('untagged test fails any include expression', () => {
+  for (const expr of ['a', 'a or b', 'a || b', 'a and b', 'a && b', '*']) {
+    assert.strictEqual(matches(expr), false);
+  }
+});
+
+test("'not X' against an untagged test is true", () => {
+  for (const expr of ['not a', '!a']) {
+    assert.strictEqual(matches(expr), true);
+  }
+});
+
+test('multiple filters AND together', () => {
+  const f1 = parseTagFilterExpression('a', 'expr');
+  const f2 = parseTagFilterExpression('not b', 'expr');
+  assert.strictEqual(evaluateTagFilters([f1, f2], tagSet('a')), true);
+  assert.strictEqual(evaluateTagFilters([f1, f2], tagSet('a', 'b')), false);
+  assert.strictEqual(evaluateTagFilters([f1, f2], tagSet('b')), false);
+  assert.strictEqual(evaluateTagFilters([f1, f2], tagSet()), false);
+});
+
+test('empty filter list always passes', () => {
+  assert.strictEqual(evaluateTagFilters([], tagSet()), true);
+  assert.strictEqual(evaluateTagFilters([], tagSet('a')), true);
+});
+
+// --- Malformed expressions -------------------------------------------------
+
+function expectInvalid(expr) {
+  assert.throws(
+    () => parseTagFilterExpression(expr, 'expr'),
+    { code: 'ERR_INVALID_ARG_VALUE' },
+    `expected '${expr}' to be invalid`,
+  );
+}
+
+test('rejects empty / whitespace-only expressions', () => {
+  for (const expr of ['', '   ', '\t\n']) {
+    expectInvalid(expr);
+  }
+});
+
+test('rejects unbalanced parentheses', () => {
+  for (const expr of ['(', '((', '(a', 'a)', '((a)', '(a))']) {
+    expectInvalid(expr);
+  }
+});
+
+test('rejects dangling operators', () => {
+  for (const expr of ['not', 'a and', 'a or', '&& a', '|| a', 'a &&', 'a ||']) {
+    expectInvalid(expr);
+  }
+});
+
+test('rejects two adjacent identifiers', () => {
+  expectInvalid('foo bar');
+});
+
+test('rejects single & and single |', () => {
+  for (const expr of ['a & b', 'a | b']) {
+    expectInvalid(expr);
+  }
+});
+
+test('rejects empty parentheses', () => {
+  expectInvalid('()');
+});
+
+test('rejects non-string expressions', () => {
+  for (const expr of [42, null, undefined, true, [], {}, Symbol('s')]) {
+    assert.throws(
+      () => parseTagFilterExpression(expr, 'expr'),
+      { code: 'ERR_INVALID_ARG_TYPE' },
+      `expected ${String(expr)} to be rejected`,
+    );
+  }
+});
diff --git a/test/parallel/test-runner-tags-events.mjs b/test/parallel/test-runner-tags-events.mjs
index 2f275cf876f97c..94bb585b67c365 100644
--- a/test/parallel/test-runner-tags-events.mjs
+++ b/test/parallel/test-runner-tags-events.mjs
@@ -93,4 +93,12 @@ describe('tag-bearing event payloads', { concurrency: false }, () => {
     // eslint-disable-next-line no-unused-vars
     for await (const _ of stream);
   });
+
+  it('process isolation forwards --experimental-test-tag-filter to children', async () => {
+    const stream = run({ files: [fixture], testTagFilters: ['not nonexistent'] });
+    stream.on('test:fail', common.mustNotCall());
+    stream.on('test:pass', common.mustCall(13));
+    // eslint-disable-next-line no-unused-vars
+    for await (const _ of stream);
+  });
 });
diff --git a/test/parallel/test-runner-tags-experimental-warning.mjs b/test/parallel/test-runner-tags-experimental-warning.mjs
index 522cc781ed3e5d..4fbe46fd144a7e 100644
--- a/test/parallel/test-runner-tags-experimental-warning.mjs
+++ b/test/parallel/test-runner-tags-experimental-warning.mjs
@@ -50,7 +50,7 @@ test('--experimental-test-tag-filter fires the warning', () => {
   const { stderr } = runChild([
     '--test',
     '--test-reporter=tap',
-    '--experimental-test-tag-filter=db',
+    '--experimental-test-tag-filter=*',
     '--test-isolation=none',
     fixture,
   ]);
diff --git a/test/parallel/test-runner-tags-validation.mjs b/test/parallel/test-runner-tags-validation.mjs
index 4e024947962700..3b6138bbf78265 100644
--- a/test/parallel/test-runner-tags-validation.mjs
+++ b/test/parallel/test-runner-tags-validation.mjs
@@ -37,6 +37,26 @@ test('empty-string tag throws ERR_INVALID_ARG_VALUE', () => {
   );
 });
 
+test('forbidden characters throw ERR_INVALID_ARG_VALUE', () => {
+  for (const bad of ['a b', 'a\tb', 'a\nb', 'a&b', 'a|b', 'a!b', 'a(b', 'a)b', 'a*b', '*', '&&', '||']) {
+    assert.throws(
+      () => test('x', { tags: [bad] }, () => {}),
+      { code: 'ERR_INVALID_ARG_VALUE' },
+      `expected throw for tag=${JSON.stringify(bad)}`,
+    );
+  }
+});
+
+test('reserved words throw ERR_INVALID_ARG_VALUE in any casing', () => {
+  for (const word of ['and', 'AND', 'And', 'or', 'OR', 'Or', 'not', 'NOT', 'Not']) {
+    assert.throws(
+      () => test('x', { tags: [word] }, () => {}),
+      { code: 'ERR_INVALID_ARG_VALUE' },
+      `expected throw for reserved word ${word}`,
+    );
+  }
+});
+
 test('Unicode and most punctuation are allowed', () => {
   // None of these should throw.
   test('unicode-1', { tags: ['café'] }, () => {});
@@ -80,7 +100,7 @@ test('suite() and describe() validate tags identically', () => {
     { code: 'ERR_INVALID_ARG_TYPE' },
   );
   assert.throws(
-    () => describe('s', { tags: [''] }, () => {}),
+    () => describe('s', { tags: ['and'] }, () => {}),
     { code: 'ERR_INVALID_ARG_VALUE' },
   );
 });
@@ -92,6 +112,13 @@ test('it() validates tags identically to test()', () => {
   );
 });
 
+test('it() validates tags identically to test()', () => {
+  assert.throws(
+    () => it('i', { tags: ['a b'] }, () => {}),
+    { code: 'ERR_INVALID_ARG_VALUE' },
+  );
+});
+
 test('run() rejects non-string testTagFilters values', () => {
   for (const bad of [[42], [{}], [null], [undefined], [true], [Symbol('s')]]) {
     assert.throws(