diff --git a/packages/codemode/src/stdlib/json.ts b/packages/codemode/src/stdlib/json.ts
index 1fe0bc5189..3ac871912d 100644
--- a/packages/codemode/src/stdlib/json.ts
+++ b/packages/codemode/src/stdlib/json.ts
@@ -96,26 +96,35 @@ const stringify = <R>(
   const apply = applyCollectionCallback(runner, replacer, "JSON.stringify", node)
   const root: SafeObject = Object.create(null) as SafeObject
   root[""] = input
+  const stack = new Set<object>()
   const visit = (holder: SafeObject | Array<unknown>, key: string): Effect.Effect<unknown, unknown, R> =>
     Effect.gen(function* () {
       const value = yield* apply([key, toJSONValue(holder[key as keyof typeof holder])])
+      if (value === undefined || typeofValue(value) === "function") return undefined
       copyIn(value, "JSON.stringify replacer result", true)
-      if (value === undefined) return undefined
       if (typeof value === "number") return Number.isFinite(value) ? value : null
       if (value === null || typeof value === "string" || typeof value === "boolean") return value
       if (Array.isArray(value)) {
+        if (stack.has(value))
+          throw new InterpreterRuntimeError("Converting circular structure to JSON.", node).as("TypeError")
+        stack.add(value)
         const result: Array<unknown> = []
         for (let index = 0; index < value.length; index += 1) {
           result.push((yield* visit(value, String(index))) ?? null)
         }
+        stack.delete(value)
         return result
       }
       if (!isPlainObject(value)) return {}
+      if (stack.has(value))
+        throw new InterpreterRuntimeError("Converting circular structure to JSON.", node).as("TypeError")
+      stack.add(value)
       const result: SafeObject = Object.create(null) as SafeObject
       for (const name of Object.keys(value)) {
         const item = yield* visit(value, name)
         if (item !== undefined) result[name] = item
       }
+      stack.delete(value)
       return result
     })
 
diff --git a/packages/codemode/test/json-callbacks-test262.test.ts b/packages/codemode/test/json-callbacks-test262.test.ts
index 4993dc44bb..b3741020b4 100644
--- a/packages/codemode/test/json-callbacks-test262.test.ts
+++ b/packages/codemode/test/json-callbacks-test262.test.ts
@@ -10,7 +10,9 @@
  * - test/built-ins/JSON/stringify/replacer-array-wrong-type.js
  * - test/built-ins/JSON/stringify/replacer-function-abrupt.js
  * - test/built-ins/JSON/stringify/replacer-function-arguments.js
+ * - test/built-ins/JSON/stringify/replacer-function-array-circular.js
  * - test/built-ins/JSON/stringify/replacer-function-object-deleted-property.js
+ * - test/built-ins/JSON/stringify/replacer-function-object-circular.js
  * - test/built-ins/JSON/stringify/replacer-function-result-undefined.js
  * - test/built-ins/JSON/stringify/replacer-function-result.js
  *
@@ -27,6 +29,7 @@
 import { describe, expect, test } from "bun:test"
 import { Effect } from "effect"
 import { CodeMode } from "../src/index.js"
+import { invokeJsonMethod } from "../src/stdlib/json.js"
 
 const value = async (code: string) => {
   const result = await Effect.runPromise(CodeMode.execute({ code, tools: {} }))
@@ -132,6 +135,40 @@ describe("Test262 JSON.stringify replacer adaptations", () => {
     ).toBe('{"a":1,"b":"<replaced>"}')
   })
 
+  test("test/built-ins/JSON/stringify/replacer-function-object-circular.js", async () => {
+    expect(
+      await value(`
+        const direct = { prop: {} }
+        const indirect = { p1: { p2: {} } }
+        const errors = []
+        try { JSON.stringify(direct, () => direct) } catch (error) { errors.push(error.name) }
+        try {
+          JSON.stringify(indirect, (key, item) => key === "p2" ? indirect : item)
+        } catch (error) { errors.push(error.name) }
+        return errors
+      `),
+    ).toEqual(["TypeError", "TypeError"])
+  })
+
+  test("test/built-ins/JSON/stringify/replacer-function-array-circular.js", async () => {
+    expect(
+      await value(`
+        const circular = [{}]
+        try { JSON.stringify(circular, () => circular) } catch (error) { return error.name }
+        return "missed"
+      `),
+    ).toBe("TypeError")
+  })
+
+  test("repeated objects outside the active ancestor chain are not circular", async () => {
+    expect(
+      await value(`
+        const shared = { value: 1 }
+        return JSON.stringify({ left: shared, right: shared }, (key, item) => item)
+      `),
+    ).toBe('{"left":{"value":1},"right":{"value":1}}')
+  })
+
   test("function replacers replace values and map undefined to omission or null", async () => {
     expect(
       await value(`return JSON.stringify({ a: 1, nested: { b: [1] } }, (key, item) => item === 1 ? undefined : item)`),
@@ -140,6 +177,19 @@ describe("Test262 JSON.stringify replacer adaptations", () => {
     expect(await value(`return JSON.stringify(1, () => undefined) === undefined`)).toBe(true)
   })
 
+  test("callable replacer results follow JSON omission semantics", async () => {
+    expect(
+      await value(`
+        const fn = () => 1
+        return [
+          JSON.stringify({ user: 1, builtin: 2 }, (key, item) => key === "user" ? fn : key === "builtin" ? Math.abs : item),
+          JSON.stringify([1, 2], (key, item) => key === "0" ? fn : key === "1" ? Number : item),
+          JSON.stringify(null, () => "abc".includes) === undefined,
+        ]
+      `),
+    ).toEqual(["{}", "[null,null]", true])
+  })
+
   test("built-in toJSON conversion runs before the function replacer", async () => {
     expect(
       await value(`
@@ -168,18 +218,26 @@ describe("CodeMode JSON callback boundaries", () => {
     expect(result).toMatchObject({ ok: false, error: { kind: "UnsupportedSyntax" } })
   })
 
-  test("blocked keys are rejected before callbacks can expose them", async () => {
+  test("blocked parse keys are rejected before reviver traversal", async () => {
     expect(
-      await value(`
-        let parseBlocked = false
-        let stringifyBlocked = false
-        try { JSON.parse('{"__proto__":1}', (key, item) => item) } catch (error) { parseBlocked = true }
-        try {
-          const input = JSON.parse('{"constructor":1}')
-          JSON.stringify(input, (key, item) => item)
-        } catch (error) { stringifyBlocked = true }
-        return [parseBlocked, stringifyBlocked]
-      `),
-    ).toEqual([true, true])
+      await value(
+        `try { JSON.parse('{"__proto__":1}', (key, item) => item) } catch (error) { return true } return false`,
+      ),
+    ).toBe(true)
+  })
+
+  test("JSON.stringify directly rejects blocked input keys", () => {
+    expect(() =>
+      invokeJsonMethod(
+        {
+          invokeFunction: () => Effect.die("unused"),
+          invokeCallable: () => Effect.die("unused"),
+          settlePromise: () => Effect.die("unused"),
+        },
+        "stringify",
+        [Object.fromEntries([["constructor", 1]])],
+        { type: "CallExpression" },
+      ),
+    ).toThrow("blocked property 'constructor'")
   })
 })