From 7e88ec58405e88fd38d0281bf59e97a1dea8429b Mon Sep 17 00:00:00 2001
From: Chris Wilkinson <chris@prereview.org>
Date: Mon, 20 Jul 2026 10:07:32 +0100
Subject: [PATCH 1/2] Refine existing type in Predicated.isTagged

---
 .changeset/funny-drinks-scream.md         | 5 +++++
 packages/effect/src/Predicate.ts          | 4 ++--
 packages/effect/typetest/Predicate.tst.ts | 8 +++++++-
 3 files changed, 14 insertions(+), 3 deletions(-)
 create mode 100644 .changeset/funny-drinks-scream.md

diff --git a/.changeset/funny-drinks-scream.md b/.changeset/funny-drinks-scream.md
new file mode 100644
index 00000000000..cb582701040
--- /dev/null
+++ b/.changeset/funny-drinks-scream.md
@@ -0,0 +1,5 @@
+---
+"effect": patch
+---
+
+Refine existing type in Predicated.isTagged
diff --git a/packages/effect/src/Predicate.ts b/packages/effect/src/Predicate.ts
index b5ac5040cdc..b6f10388a4d 100644
--- a/packages/effect/src/Predicate.ts
+++ b/packages/effect/src/Predicate.ts
@@ -1164,8 +1164,8 @@ export const hasProperty: {
  * @since 2.0.0
  */
 export const isTagged: {
-  <K extends string>(tag: K): (self: unknown) => self is { _tag: K }
-  <K extends string>(self: unknown, tag: K): self is { _tag: K }
+  <K extends string>(tag: K): <T>(self: T) => self is T extends {} ? Extract<T, { _tag: K }> : T & { _tag: K }
+  <K extends string, T>(self: T, tag: K): self is T extends {} ? Extract<T, { _tag: K }> : T & { _tag: K }
 } = dual(
   2,
   <K extends string>(self: unknown, tag: K): self is { _tag: K } => hasProperty(self, "_tag") && self["_tag"] === tag
diff --git a/packages/effect/typetest/Predicate.tst.ts b/packages/effect/typetest/Predicate.tst.ts
index dc74a61d31d..a891aa33818 100644
--- a/packages/effect/typetest/Predicate.tst.ts
+++ b/packages/effect/typetest/Predicate.tst.ts
@@ -7,6 +7,8 @@ declare const unknowns: ReadonlyArray<unknown>
 declare const numberOrNull: ReadonlyArray<number | null>
 declare const numberOrUndefined: ReadonlyArray<number | undefined>
 declare const numberOrNullOrUndefined: ReadonlyArray<number | null | undefined>
+declare const tags: ReadonlyArray<{ _tag: "a"; a: string } | { _tag: "b"; b: string }>
+declare const tagsOrNumbers: ReadonlyArray<{ _tag: "a"; a: string } | { _tag: "b"; b: string } | number>
 
 describe("Predicate", () => {
   it("isString", () => {
@@ -56,7 +58,11 @@ describe("Predicate", () => {
   })
 
   it("isTagged", () => {
-    expect(anys.filter(Predicate.isTagged("a"))).type.toBe<Array<{ _tag: "a" }>>()
+    expect(anys.filter(Predicate.isTagged("a"))).type.toBe<Array<any>>()
+    expect(unknowns.filter(Predicate.isTagged("a"))).type.toBe<Array<{ _tag: "a" }>>()
+    expect(tags.filter(Predicate.isTagged("a"))).type.toBe<Array<{ _tag: "a"; a: string }>>()
+    expect(tagsOrNumbers.filter(Predicate.isTagged("a"))).type.toBe<Array<{ _tag: "a"; a: string }>>()
+    expect(numberOrNull.filter(Predicate.isTagged("a"))).type.toBe<Array<never>>()
   })
 
   it("isNullish", () => {

From 78253379423a57e36cdf0f0c07601747a6f0e5e5 Mon Sep 17 00:00:00 2001
From: Chris Wilkinson <chris@prereview.org>
Date: Mon, 20 Jul 2026 10:20:10 +0100
Subject: [PATCH 2/2] Correct module name

---
 .changeset/funny-drinks-scream.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/.changeset/funny-drinks-scream.md b/.changeset/funny-drinks-scream.md
index cb582701040..4428ac8ba31 100644
--- a/.changeset/funny-drinks-scream.md
+++ b/.changeset/funny-drinks-scream.md
@@ -2,4 +2,4 @@
 "effect": patch
 ---
 
-Refine existing type in Predicated.isTagged
+Refine existing type in Predicate.isTagged