diff --git a/eslint-factory/eslint.config.cjs b/eslint-factory/eslint.config.cjs
index eb245431bde..08ac9d9159d 100644
--- a/eslint-factory/eslint.config.cjs
+++ b/eslint-factory/eslint.config.cjs
@@ -13,6 +13,7 @@ module.exports = [
     },
     rules: {
       "gh-aw-custom/no-core-setoutput-non-string": "warn",
+      "gh-aw-custom/no-json-stringify-error": "warn",
       "gh-aw-custom/no-unsafe-catch-error-property": "warn",
       "gh-aw-custom/no-unsafe-promise-catch-error-property": "warn",
       "gh-aw-custom/prefer-get-error-message": "warn",
diff --git a/eslint-factory/src/index.ts b/eslint-factory/src/index.ts
index 0f66a326b19..b4ac4e27a50 100644
--- a/eslint-factory/src/index.ts
+++ b/eslint-factory/src/index.ts
@@ -1,4 +1,5 @@
 import { noCoreSetOutputNonStringRule } from "./rules/no-core-setoutput-non-string";
+import { noJsonStringifyErrorRule } from "./rules/no-json-stringify-error";
 import { noUnsafeCatchErrorPropertyRule } from "./rules/no-unsafe-catch-error-property";
 import { noUnsafePromiseCatchErrorPropertyRule } from "./rules/no-unsafe-promise-catch-error-property";
 import { preferGetErrorMessageRule } from "./rules/prefer-get-error-message";
@@ -15,6 +16,7 @@ const plugin = {
   },
   rules: {
     "no-core-setoutput-non-string": noCoreSetOutputNonStringRule,
+    "no-json-stringify-error": noJsonStringifyErrorRule,
     "no-unsafe-catch-error-property": noUnsafeCatchErrorPropertyRule,
     "no-unsafe-promise-catch-error-property": noUnsafePromiseCatchErrorPropertyRule,
     "prefer-get-error-message": preferGetErrorMessageRule,
diff --git a/eslint-factory/src/rules/no-json-stringify-error.test.ts b/eslint-factory/src/rules/no-json-stringify-error.test.ts
new file mode 100644
index 00000000000..0b58fd18d2f
--- /dev/null
+++ b/eslint-factory/src/rules/no-json-stringify-error.test.ts
@@ -0,0 +1,233 @@
+import { RuleTester } from "eslint";
+import { describe, it } from "vitest";
+import { noJsonStringifyErrorRule } from "./no-json-stringify-error";
+
+const cjsRuleTester = new RuleTester({
+  languageOptions: {
+    ecmaVersion: 2022,
+    sourceType: "commonjs",
+  },
+});
+
+const esmRuleTester = new RuleTester({
+  languageOptions: {
+    ecmaVersion: 2022,
+    sourceType: "module",
+  },
+});
+
+describe("no-json-stringify-error", () => {
+  it("valid: JSON.stringify on a non-caught variable is not flagged", () => {
+    cjsRuleTester.run("no-json-stringify-error", noJsonStringifyErrorRule, {
+      valid: [`const obj = { a: 1 }; JSON.stringify(obj);`, `JSON.stringify({ message: "hello" });`, `JSON.stringify("a string");`, `const data = fetchData(); JSON.stringify(data);`],
+      invalid: [],
+    });
+  });
+
+  it("valid: JSON.stringify on a non-error variable inside a catch block is not flagged", () => {
+    cjsRuleTester.run("no-json-stringify-error", noJsonStringifyErrorRule, {
+      valid: [`try { f(); } catch (err) { const data = { a: 1 }; JSON.stringify(data); }`, `try { f(); } catch (err) { JSON.stringify(someOtherVar); }`, `try { f(); } catch (err) { JSON.stringify({ message: err.message }); }`],
+      invalid: [],
+    });
+  });
+
+  it("valid: JSON.stringify with explicit error properties is not flagged", () => {
+    cjsRuleTester.run("no-json-stringify-error", noJsonStringifyErrorRule, {
+      valid: [`try { f(); } catch (err) { JSON.stringify({ message: err.message, stack: err.stack }); }`, `try { f(); } catch (err) { JSON.stringify({ error: String(err) }); }`],
+      invalid: [],
+    });
+  });
+
+  it("valid: JSON.stringify on catch param that shadows outer scope is not flagged outside the catch", () => {
+    cjsRuleTester.run("no-json-stringify-error", noJsonStringifyErrorRule, {
+      valid: [
+        `const err = { a: 1 }; try { f(); } catch (err) { } JSON.stringify(err);`,
+        `try { f(); } catch (err) { [1].forEach(function(err) { JSON.stringify(err); }); }`,
+        `try { f(); } catch (err) { items.map(err => JSON.stringify(err)); }`,
+      ],
+      invalid: [],
+    });
+  });
+
+  it("valid: JSON.stringify on promise .catch() non-error param is not flagged", () => {
+    cjsRuleTester.run("no-json-stringify-error", noJsonStringifyErrorRule, {
+      valid: [`p.catch(function(err) { JSON.stringify(otherVar); })`, `p.catch(err => JSON.stringify(notErr))`],
+      invalid: [],
+    });
+  });
+
+  it("valid: bare catch {} without binding is not flagged", () => {
+    cjsRuleTester.run("no-json-stringify-error", noJsonStringifyErrorRule, {
+      valid: [`try { f(); } catch { JSON.stringify(someObj); }`],
+      invalid: [],
+    });
+  });
+
+  it("invalid: JSON.stringify(err) in catch block is flagged", () => {
+    cjsRuleTester.run("no-json-stringify-error", noJsonStringifyErrorRule, {
+      valid: [],
+      invalid: [
+        {
+          code: `try { f(); } catch (err) { core.error(JSON.stringify(err)); }`,
+          errors: [
+            {
+              messageId: "jsonStringifyError",
+              data: { errorVar: "err" },
+              suggestions: [
+                {
+                  messageId: "useGetErrorMessage",
+                  data: { errorVar: "err" },
+                  output: `try { f(); } catch (err) { core.error(getErrorMessage(err)); }`,
+                },
+              ],
+            },
+          ],
+        },
+      ],
+    });
+  });
+
+  it("invalid: JSON.stringify(error, null, 2) in catch block is flagged", () => {
+    cjsRuleTester.run("no-json-stringify-error", noJsonStringifyErrorRule, {
+      valid: [],
+      invalid: [
+        {
+          code: `try { f(); } catch (error) { core.error(\`details: \${JSON.stringify(error, null, 2)}\`); }`,
+          errors: [
+            {
+              messageId: "jsonStringifyError",
+              data: { errorVar: "error" },
+              suggestions: [
+                {
+                  messageId: "useGetErrorMessage",
+                  data: { errorVar: "error" },
+                  output: `try { f(); } catch (error) { core.error(\`details: \${getErrorMessage(error)}\`); }`,
+                },
+              ],
+            },
+          ],
+        },
+      ],
+    });
+  });
+
+  it("invalid: JSON.stringify(err) in promise .catch() arrow callback is flagged", () => {
+    cjsRuleTester.run("no-json-stringify-error", noJsonStringifyErrorRule, {
+      valid: [],
+      invalid: [
+        {
+          code: `p.catch(err => core.error(JSON.stringify(err)));`,
+          errors: [
+            {
+              messageId: "jsonStringifyError",
+              data: { errorVar: "err" },
+              suggestions: [
+                {
+                  messageId: "useGetErrorMessage",
+                  data: { errorVar: "err" },
+                  output: `p.catch(err => core.error(getErrorMessage(err)));`,
+                },
+              ],
+            },
+          ],
+        },
+      ],
+    });
+  });
+
+  it("invalid: JSON.stringify(err) in promise .catch() function callback is flagged", () => {
+    cjsRuleTester.run("no-json-stringify-error", noJsonStringifyErrorRule, {
+      valid: [],
+      invalid: [
+        {
+          code: `p.catch(function(err) { core.error(JSON.stringify(err)); });`,
+          errors: [
+            {
+              messageId: "jsonStringifyError",
+              data: { errorVar: "err" },
+              suggestions: [
+                {
+                  messageId: "useGetErrorMessage",
+                  data: { errorVar: "err" },
+                  output: `p.catch(function(err) { core.error(getErrorMessage(err)); });`,
+                },
+              ],
+            },
+          ],
+        },
+      ],
+    });
+  });
+
+  it("invalid: nested catch — each catch variable is tracked independently", () => {
+    cjsRuleTester.run("no-json-stringify-error", noJsonStringifyErrorRule, {
+      valid: [],
+      invalid: [
+        {
+          code: `try { f(); } catch (outer) { try { g(); } catch (inner) { } core.error(JSON.stringify(outer)); }`,
+          errors: [
+            {
+              messageId: "jsonStringifyError",
+              data: { errorVar: "outer" },
+              suggestions: [
+                {
+                  messageId: "useGetErrorMessage",
+                  data: { errorVar: "outer" },
+                  output: `try { f(); } catch (outer) { try { g(); } catch (inner) { } core.error(getErrorMessage(outer)); }`,
+                },
+              ],
+            },
+          ],
+        },
+      ],
+    });
+  });
+
+  it("invalid: works with ES module syntax", () => {
+    esmRuleTester.run("no-json-stringify-error", noJsonStringifyErrorRule, {
+      valid: [],
+      invalid: [
+        {
+          code: `try { fetch(url); } catch (e) { console.error(JSON.stringify(e)); }`,
+          errors: [
+            {
+              messageId: "jsonStringifyError",
+              data: { errorVar: "e" },
+              suggestions: [
+                {
+                  messageId: "useGetErrorMessage",
+                  data: { errorVar: "e" },
+                  output: `try { fetch(url); } catch (e) { console.error(getErrorMessage(e)); }`,
+                },
+              ],
+            },
+          ],
+        },
+      ],
+    });
+  });
+
+  it("invalid: inner catch variable also flagged when outer has JSON.stringify", () => {
+    cjsRuleTester.run("no-json-stringify-error", noJsonStringifyErrorRule, {
+      valid: [],
+      invalid: [
+        {
+          code: `try { f(); } catch (outer) { try { g(); } catch (inner) { core.error(JSON.stringify(inner)); } }`,
+          errors: [
+            {
+              messageId: "jsonStringifyError",
+              data: { errorVar: "inner" },
+              suggestions: [
+                {
+                  messageId: "useGetErrorMessage",
+                  data: { errorVar: "inner" },
+                  output: `try { f(); } catch (outer) { try { g(); } catch (inner) { core.error(getErrorMessage(inner)); } }`,
+                },
+              ],
+            },
+          ],
+        },
+      ],
+    });
+  });
+});
diff --git a/eslint-factory/src/rules/no-json-stringify-error.ts b/eslint-factory/src/rules/no-json-stringify-error.ts
new file mode 100644
index 00000000000..6da57870020
--- /dev/null
+++ b/eslint-factory/src/rules/no-json-stringify-error.ts
@@ -0,0 +1,131 @@
+import { AST_NODE_TYPES, ESLintUtils, TSESTree } from "@typescript-eslint/utils";
+
+const createRule = ESLintUtils.RuleCreator(name => `https://github.com/github/gh-aw/tree/main/eslint-factory#${name}`);
+
+interface ErrorScope {
+  varName: string;
+  isSentinel: boolean;
+}
+
+/**
+ * Returns true when the function is passed directly as the first argument to a
+ * `.catch()` call. Named-reference handlers (for example `p.catch(handler)`)
+ * are intentionally out of scope.
+ */
+function isCatchCallback(node: TSESTree.ArrowFunctionExpression | TSESTree.FunctionExpression): boolean {
+  const parent = node.parent;
+  if (!parent || parent.type !== AST_NODE_TYPES.CallExpression) return false;
+  const callee = parent.callee;
+  if (callee.type !== AST_NODE_TYPES.MemberExpression || callee.computed) return false;
+  const prop = callee.property;
+  return prop.type === AST_NODE_TYPES.Identifier && prop.name === "catch" && parent.arguments[0] === node;
+}
+
+export const noJsonStringifyErrorRule = createRule({
+  name: "no-json-stringify-error",
+  meta: {
+    type: "problem",
+    hasSuggestions: true,
+    docs: {
+      description: "Disallow JSON.stringify() on caught error variables — Error properties (message, stack, etc.) are non-enumerable and produce {} silently",
+    },
+    schema: [],
+    messages: {
+      jsonStringifyError:
+        "JSON.stringify({{errorVar}}) produces {} for Error objects — Error properties (message, stack, etc.) are non-enumerable. Prefer getErrorMessage({{errorVar}}) from error_helpers.cjs or explicitly serialize a guarded value after narrowing it.",
+      useGetErrorMessage: "Replace with getErrorMessage({{errorVar}}) — ensure getErrorMessage is imported from error_helpers.cjs.",
+    },
+  },
+  defaultOptions: [],
+  create(context) {
+    // Stack tracking caught error variable names.
+    // Each scope entry holds varName (empty string for sentinel) and isSentinel flag.
+    const scopeStack: ErrorScope[] = [];
+
+    function getCaughtVarNames(): Set<string> {
+      const names = new Set<string>();
+      // Walk from the innermost active scope outward and stop at the first
+      // sentinel so non-.catch() callbacks cannot see shadowed catch vars.
+      for (let i = scopeStack.length - 1; i >= 0; i--) {
+        const scope = scopeStack[i];
+        if (scope.isSentinel) break;
+        if (scope.varName) names.add(scope.varName);
+      }
+      return names;
+    }
+
+    function enterFunction(node: TSESTree.ArrowFunctionExpression | TSESTree.FunctionExpression): void {
+      if (isCatchCallback(node)) {
+        const params = node.params;
+        if (params.length === 1 && params[0].type === AST_NODE_TYPES.Identifier) {
+          scopeStack.push({ varName: params[0].name, isSentinel: false });
+        } else {
+          // No-param or destructuring: push sentinel so outer frames are not affected
+          scopeStack.push({ varName: "", isSentinel: true });
+        }
+      } else {
+        // Non-.catch() function: sentinel to avoid false positives from shadowed names
+        scopeStack.push({ varName: "", isSentinel: true });
+      }
+    }
+
+    function exitFunction(): void {
+      scopeStack.pop();
+    }
+
+    return {
+      // Track catch clause parameters
+      CatchClause(node) {
+        const param = node.param;
+        if (!param || param.type !== AST_NODE_TYPES.Identifier) {
+          scopeStack.push({ varName: "", isSentinel: true });
+        } else {
+          scopeStack.push({ varName: param.name, isSentinel: false });
+        }
+      },
+      "CatchClause:exit"() {
+        scopeStack.pop();
+      },
+
+      // Track .catch() callback parameters
+      ArrowFunctionExpression: enterFunction,
+      "ArrowFunctionExpression:exit": exitFunction,
+      FunctionExpression: enterFunction,
+      "FunctionExpression:exit": exitFunction,
+
+      // Detect JSON.stringify(caughtErrorVar, ...)
+      CallExpression(node) {
+        const caughtNames = getCaughtVarNames();
+        if (caughtNames.size === 0) return;
+
+        const callee = node.callee;
+        if (callee.type !== AST_NODE_TYPES.MemberExpression) return;
+        if (callee.computed) return;
+        const obj = callee.object;
+        const prop = callee.property;
+        if (obj.type !== AST_NODE_TYPES.Identifier || obj.name !== "JSON") return;
+        if (prop.type !== AST_NODE_TYPES.Identifier || prop.name !== "stringify") return;
+
+        const firstArg = node.arguments[0];
+        if (!firstArg || firstArg.type !== AST_NODE_TYPES.Identifier) return;
+        if (!caughtNames.has(firstArg.name)) return;
+
+        const errorVar = firstArg.name;
+        context.report({
+          node,
+          messageId: "jsonStringifyError",
+          data: { errorVar },
+          suggest: [
+            {
+              messageId: "useGetErrorMessage" as const,
+              data: { errorVar },
+              fix(fixer) {
+                return fixer.replaceText(node, `getErrorMessage(${errorVar})`);
+              },
+            },
+          ],
+        });
+      },
+    };
+  },
+});