Add eslint-plugin-yamllint for YAML 1.1 safety

.github/actions/pnpm-resolve-pinned/action.yml

@@ -1,3 +1,4 @@
+---
 description: Resolve a package's locked version from pnpm-lock.yaml (no install required)
 inputs:
   package:

.github/actions/pnpm-tasks/action.yml

@@ -1,3 +1,4 @@
+---
 description: Set up pnpm and Node.js, restore cache, and install dependencies
 inputs:
   commands:

.github/actions/turbo-run/action.yml

@@ -1,3 +1,4 @@
+---
 description: Run a turbo task, skipping pnpm install on full cache hit
 inputs:
   task:

.github/workflows/cd.yml

@@ -1,3 +1,4 @@
+---
 env:
   FORCE_JAVASCRIPT_ACTIONS_TO_NODE24: true
 

.github/workflows/changeset-check.yml

@@ -1,3 +1,4 @@
+---
 env:
   FORCE_JAVASCRIPT_ACTIONS_TO_NODE24: true
 

.github/workflows/ci.yml

@@ -1,3 +1,4 @@
+---
 env:
   FORCE_JAVASCRIPT_ACTIONS_TO_NODE24: true
 

.github/workflows/pre-commit-seed.yml

@@ -1,3 +1,4 @@
+---
 env:
   FORCE_JAVASCRIPT_ACTIONS_TO_NODE24: true
   # Pin prek cache to a known path for reliable GitHub Actions caching

.github/workflows/pre-commit.yml

@@ -1,3 +1,4 @@
+---
 env:
   FORCE_JAVASCRIPT_ACTIONS_TO_NODE24: true
   # Pin prek cache to a known path for reliable GitHub Actions caching

AGENTS.md

@@ -22,6 +22,7 @@ packages/
   cli/                          — @gtbuchanan/cli (gtb build CLI for consumers)
   eslint-config/                — @gtbuchanan/eslint-config (ESLint configure())
   eslint-plugin-markdownlint/   — @gtbuchanan/eslint-plugin-markdownlint (markdownlint via ESLint)
+  eslint-plugin-yamllint/       — @gtbuchanan/eslint-plugin-yamllint (yamllint gap rules via ESLint)
   tsconfig/                     — @gtbuchanan/tsconfig (shared base tsconfig.json)
   vitest-config/                — @gtbuchanan/vitest-config (configurePackage, configureGlobal, + e2e variants)
   test-utils/                   — private shared E2E fixture utilities
@@ -117,6 +118,8 @@ globs for monorepos, or falls back to single-package mode.
   `eslint-plugin-import-x` (ordering), `@eslint/json` (JSON linting),
   `eslint-plugin-pnpm` (workspace validation), `eslint-plugin-n` (Node.js
   rules), `eslint-plugin-yml` (YAML linting + key sorting),
+  `eslint-plugin-yamllint` (yamllint gap rules: truthy, octal-values,
+  anchors, document-start/end),
   `eslint-plugin-markdownlint` (Markdown structural linting),
   `@vitest/eslint-plugin` (test rules), and `eslint-plugin-only-warn`
   (downgrades errors to warnings).
@@ -261,6 +264,9 @@ Consumer guidance:
   `<!-- markdownlint-disable-next-line MD024 -->`. This keeps the
   plugin compatible with standalone markdownlint usage.
 - All exported functions, types, interfaces, and constants must have JSDoc comments.
+- When adding or removing a package, update the packages table in
+  `README.md`, the structure tree above, and the linter/formatter
+  sections as applicable.
 - When asserting on `CommandResult` (exit code, stdout, stderr), use
   `expect(result).toMatchObject({ exitCode: 0 })` instead of
   `expect(result.exitCode).toBe(0)`. On failure, `toMatchObject` shows

README.md

@@ -9,6 +9,7 @@ Shared build configuration monorepo for JavaScript/TypeScript projects.
 | [@gtbuchanan/cli](packages/cli)                                               | Shared build CLI (`gtb`)             |
 | [@gtbuchanan/eslint-config](packages/eslint-config)                           | Shared ESLint configuration          |
 | [@gtbuchanan/eslint-plugin-markdownlint](packages/eslint-plugin-markdownlint) | ESLint plugin wrapping markdownlint  |
+| [@gtbuchanan/eslint-plugin-yamllint](packages/eslint-plugin-yamllint)         | ESLint plugin for yamllint gap rules |
 | [@gtbuchanan/tsconfig](packages/tsconfig)                                     | Shared TypeScript base configuration |
 | [@gtbuchanan/vitest-config](packages/vitest-config)                           | Shared Vitest configuration          |
 

codecov.yml

@@ -1,3 +1,4 @@
+---
 codecov:
   require_ci_to_pass: true
 comment:
@@ -18,6 +19,10 @@ component_management:
       name: test-utils
       paths:
         - packages/test-utils/src/**
+    - component_id: eslint-plugin-yamllint
+      name: eslint-plugin-yamllint
+      paths:
+        - packages/eslint-plugin-yamllint/src/**
     - component_id: eslint-plugin-markdownlint
       name: eslint-plugin-markdownlint
       paths:
@@ -53,6 +58,10 @@ flags:
     carryforward: true
     paths:
       - packages/eslint-plugin-markdownlint/
+  eslint-plugin-yamllint:
+    carryforward: true
+    paths:
+      - packages/eslint-plugin-yamllint/
   test-utils:
     carryforward: true
     paths:

packages/eslint-config/e2e/cli.test.ts

@@ -53,7 +53,10 @@ const createFixture = () => {
     depsPackages: ['typescript'],
     hookPackages: ['eslint', 'jiti'],
     packageName: '@gtbuchanan/eslint-config',
-    workspaceDeps: ['@gtbuchanan/eslint-plugin-markdownlint'],
+    workspaceDeps: [
+      '@gtbuchanan/eslint-plugin-markdownlint',
+      '@gtbuchanan/eslint-plugin-yamllint',
+    ],
   });
 
   const eslint = path.join(fixture.hookDir, 'node_modules/.bin/eslint');
@@ -222,7 +225,7 @@ describe.concurrent('eslint CLI integration', () => {
   it('formats JSON, Markdown, YAML, and CSS via Prettier plugins', async ({ fixture, expect }) => {
     const unsortedJson = '{\n  "z": 1,\n  "a": [1, 2]\n}\n';
     const longMarkdown = `# Title\n\n${'word '.repeat(40).trim()}\n`;
-    const doubleQuotedYaml = 'key: "value"\n';
+    const doubleQuotedYaml = '---\nkey: "value"\n';
     const unsortedCss = '.box {\n  display: flex;\n  color: red;\n}\n';
 
     const result = await fixture.run({
@@ -246,14 +249,24 @@ describe.concurrent('eslint CLI integration', () => {
     expect(result.readFile('doc.md')).toBe(longMarkdown);
 
     // YAML: singleQuote from prettierDefaults converts double quotes
-    expect(result.readFile('config.yml')).toBe("key: 'value'\n");
+    expect(result.readFile('config.yml')).toBe("---\nkey: 'value'\n");
 
     // CSS: alphabetical property sorting (color before display)
     expect(result.readFile('style.css')).toBe(
       '.box {\n  color: red;\n  display: flex;\n}\n',
     );
   });
 
+  it('detects yamllint violations in YAML files', async ({ fixture, expect }) => {
+    const yaml = '---\ncountry: NO\nperms: 0777\n';
+    const result = await fixture.run({
+      files: { 'config.yml': yaml },
+    });
+
+    expect(result.stdout).toContain('yamllint/truthy');
+    expect(result.stdout).toContain('yamllint/octal-values');
+  });
+
   it('detects markdownlint violations in markdown files', async ({ fixture, expect }) => {
     const result = await fixture.run({
       files: { 'doc.md': '# Title\n\n# Title\n' },

packages/eslint-config/package.json

@@ -25,6 +25,7 @@
     "@eslint-community/eslint-plugin-eslint-comments": "catalog:",
     "@eslint/json": "catalog:",
     "@gtbuchanan/eslint-plugin-markdownlint": "workspace:*",
+    "@gtbuchanan/eslint-plugin-yamllint": "workspace:*",
     "@prettier/plugin-xml": "catalog:",
     "@stylistic/eslint-plugin": "catalog:",
     "@vitest/eslint-plugin": "catalog:",

packages/eslint-config/src/plugins/index.ts

@@ -15,10 +15,11 @@ import typescript from './typescript.ts';
 import unicorn from './unicorn.ts';
 import vitest from './vitest.ts';
 import yaml from './yaml.ts';
+import yamllint from './yamllint.ts';
 
 /** Ordered plugin factories. Later entries override earlier ones for the same file. */
 export const plugins: readonly PluginFactory[] = [
-  typescript, unicorn, promise, regexp, jsdoc, json, yaml, pnpm, node,
+  typescript, unicorn, promise, regexp, jsdoc, json, yaml, yamllint, pnpm, node,
   format, markdownlint, stylistic, eslintComments, importX,
   core, vitest,
 ];

packages/eslint-config/src/plugins/yaml.ts

@@ -3,14 +3,20 @@ import type { PluginFactory } from '../index.ts';
 
 // --- YAML ---
 
-/** YAML linting configs with key sorting. */
+/** YAML linting configs with key sorting and stricter value rules. */
 const plugin: PluginFactory = () => [
   ...ymlConfigs['flat/recommended'],
   ...ymlConfigs['flat/prettier'],
   {
     files: ['**/*.yaml', '**/*.yml'],
-    // Justification: Alphabetical keys reduce merge conflicts in shared YAML configs
-    rules: { 'yml/sort-keys': 'warn' },
+    rules: {
+      // Justification: Trailing zeros obscure numeric precision intent (e.g., 1.0 vs 1)
+      'yml/no-trailing-zeros': 'warn',
+      // Justification: Non-string keys (numbers, booleans) cause subtle type coercion bugs
+      'yml/require-string-key': 'warn',
+      // Justification: Alphabetical keys reduce merge conflicts in shared YAML configs
+      'yml/sort-keys': 'warn',
+    },
   },
 ];
 

packages/eslint-config/src/plugins/yamllint.ts

@@ -0,0 +1,31 @@
+import yamllint from '@gtbuchanan/eslint-plugin-yamllint';
+import type { PluginFactory } from '../index.ts';
+
+/** yamllint-equivalent YAML rules via `@gtbuchanan/eslint-plugin-yamllint`. */
+const plugin: PluginFactory = () => [
+  {
+    files: ['**/*.yaml', '**/*.yml'],
+    plugins: { yamllint },
+    rules: {
+      'yamllint/anchors': 'warn',
+      'yamllint/document-end': 'warn',
+      'yamllint/document-start': 'warn',
+      'yamllint/octal-values': 'warn',
+      'yamllint/truthy': ['warn', {
+        'allowed-values': ['true', 'false'],
+      }],
+    },
+  },
+  {
+    /*
+     * Renovate strips document start markers from pnpm-workspace.yaml
+     * when bumping dependencies. Disable the rule to avoid noise.
+     */
+    files: ['pnpm-workspace.yaml'],
+    rules: {
+      'yamllint/document-start': 'off',
+    },
+  },
+];
+
+export default plugin;

packages/eslint-plugin-yamllint/README.md

@@ -0,0 +1,116 @@
+# @gtbuchanan/eslint-plugin-yamllint
+
+ESLint plugin implementing [yamllint](https://github.com/adrienverge/yamllint)-equivalent
+rules as native ESLint rules using the [yaml](https://eemeli.org/yaml/) npm
+package. No Python dependency required.
+
+## Why?
+
+[Prettier](https://prettier.io/) and
+[eslint-plugin-yml](https://ota-meshi.github.io/eslint-plugin-yml/) cover most
+of yamllint's rules, but several high-impact rules have no equivalent. This
+plugin fills those gaps.
+
+### yamllint rule coverage
+
+| yamllint rule           | Covered by                             | Notes                                                           |
+| ----------------------- | -------------------------------------- | --------------------------------------------------------------- |
+| anchors                 | **eslint-plugin-yamllint**             | Unused/duplicate anchors, undeclared aliases                    |
+| braces                  | eslint-plugin-yml + Prettier           |                                                                 |
+| brackets                | eslint-plugin-yml + Prettier           |                                                                 |
+| colons                  | eslint-plugin-yml + Prettier           |                                                                 |
+| commas                  | Prettier                               |                                                                 |
+| comments                | eslint-plugin-yml (partial)            | `min-spaces-from-content` not covered                           |
+| comments-indentation    | _not covered_                          |                                                                 |
+| document-end            | **eslint-plugin-yamllint**             | Require or forbid `...` markers                                 |
+| document-start          | **eslint-plugin-yamllint**             | Require or forbid `---` markers                                 |
+| empty-lines             | eslint-plugin-yml + Prettier           |                                                                 |
+| empty-values            | eslint-plugin-yml                      |                                                                 |
+| float-values            | eslint-plugin-yml (partial)            | Only trailing zeros; no leading-dot/scientific/NaN/Inf          |
+| hyphens                 | Prettier                               |                                                                 |
+| indentation             | eslint-plugin-yml + Prettier           |                                                                 |
+| key-duplicates          | YAML parser                            | Hard parse error, not configurable                              |
+| key-ordering            | eslint-plugin-yml                      | `yml/sort-keys` is a superset                                   |
+| line-length             | Prettier (partial)                     | `printWidth` is a soft target, not a hard limit                 |
+| new-line-at-end-of-file | Prettier                               |                                                                 |
+| new-lines               | Prettier                               |                                                                 |
+| octal-values            | **eslint-plugin-yamllint**             | Implicit (`0777`) and explicit (`0o777`) octals                 |
+| quoted-strings          | eslint-plugin-yml + Prettier (partial) | Basic style only; `required`/`extra-*`/`check-keys` not covered |
+| trailing-spaces         | Prettier                               |                                                                 |
+| truthy                  | **eslint-plugin-yamllint**             | Unquoted YAML 1.1 boolean-like values (auto-fixable)            |
+
+## Install
+
+```sh
+pnpm add -D @gtbuchanan/eslint-plugin-yamllint eslint
+```
+
+## Usage
+
+```typescript
+// eslint.config.ts
+import yamllint from '@gtbuchanan/eslint-plugin-yamllint';
+
+export default [
+  {
+    files: ['**/*.yaml', '**/*.yml'],
+    plugins: { yamllint },
+    rules: {
+      'yamllint/anchors': 'warn',
+      'yamllint/document-end': 'warn',
+      'yamllint/document-start': 'warn',
+      'yamllint/octal-values': 'warn',
+      'yamllint/truthy': ['warn', { 'allowed-values': ['true', 'false'] }],
+    },
+  },
+];
+```
+
+## Rules
+
+### `yamllint/truthy`
+
+Flags unquoted YAML 1.1 boolean-like values (`yes`, `no`, `on`, `off`, `y`,
+`n`, `true`, `false`, and case variants) that may be silently coerced.
+Auto-fixable — wraps values in double quotes.
+
+| Option           | Type       | Default | Description              |
+| ---------------- | ---------- | ------- | ------------------------ |
+| `allowed-values` | `string[]` | `[]`    | Values to allow unquoted |
+| `check-keys`     | `boolean`  | `false` | Also check mapping keys  |
+
+### `yamllint/octal-values`
+
+Flags implicit (`0777`) and explicit (`0o777`) YAML 1.1 octal literals that
+may be interpreted differently across YAML versions.
+
+| Option                  | Type      | Default | Description               |
+| ----------------------- | --------- | ------- | ------------------------- |
+| `forbid-implicit-octal` | `boolean` | `true`  | Flag `0777`-style octals  |
+| `forbid-explicit-octal` | `boolean` | `true`  | Flag `0o777`-style octals |
+
+### `yamllint/anchors`
+
+Detects unused anchors, duplicate anchors, and undeclared aliases.
+
+| Option                      | Type      | Default | Description                          |
+| --------------------------- | --------- | ------- | ------------------------------------ |
+| `forbid-duplicated-anchors` | `boolean` | `true`  | Flag duplicate `&name` anchors       |
+| `forbid-undeclared-aliases` | `boolean` | `true`  | Flag `*name` without matching anchor |
+| `forbid-unused-anchors`     | `boolean` | `true`  | Flag anchors with no alias reference |
+
+### `yamllint/document-start`
+
+Requires or forbids `---` document start markers. Auto-fixable.
+
+| Option    | Type      | Default | Description                                     |
+| --------- | --------- | ------- | ----------------------------------------------- |
+| `present` | `boolean` | `true`  | Require (`true`) or forbid (`false`) the marker |
+
+### `yamllint/document-end`
+
+Requires or forbids `...` document end markers. Auto-fixable.
+
+| Option    | Type      | Default | Description                                     |
+| --------- | --------- | ------- | ----------------------------------------------- |
+| `present` | `boolean` | `false` | Require (`true`) or forbid (`false`) the marker |

packages/eslint-plugin-yamllint/eslint.config.ts

@@ -0,0 +1,5 @@
+import { configure } from '../eslint-config/src/index.ts';
+
+export default configure({
+  tsconfigRootDir: import.meta.dirname,
+});

packages/eslint-plugin-yamllint/package.json

@@ -0,0 +1,42 @@
+{
+  "name": "@gtbuchanan/eslint-plugin-yamllint",
+  "version": "0.1.0",
+  "description": "ESLint plugin implementing yamllint-equivalent rules for YAML files",
+  "type": "module",
+  "imports": {
+    "#src/*": "./src/*"
+  },
+  "exports": {
+    ".": "./src/index.ts"
+  },
+  "scripts": {
+    "compile:ts": "pnpm run gtb compile:ts",
+    "coverage:codecov:upload": "pnpm run gtb coverage:codecov:upload",
+    "coverage:vitest:merge": "pnpm run gtb coverage:vitest:merge",
+    "gtb": "node --experimental-strip-types ../../packages/cli/bin/gtb.ts",
+    "lint:eslint": "pnpm run gtb lint:eslint",
+    "pack:npm": "pnpm run gtb pack:npm",
+    "test:vitest:fast": "pnpm run gtb test:vitest:fast",
+    "test:vitest:slow": "pnpm run gtb test:vitest:slow",
+    "typecheck:ts": "pnpm run gtb typecheck:ts"
+  },
+  "dependencies": {
+    "yaml": "catalog:"
+  },
+  "devDependencies": {
+    "@gtbuchanan/vitest-config": "workspace:*"
+  },
+  "peerDependencies": {
+    "eslint": "^10.0.0"
+  },
+  "engines": {
+    "node": ">=22.17"
+  },
+  "publishConfig": {
+    "directory": "dist/source",
+    "exports": {
+      ".": "./src/index.js"
+    },
+    "linkDirectory": false
+  }
+}