diff --git a/packages/core/src/api/api-result.ts b/packages/core/src/api/api-result.ts
index 6808d1673bad0..1c12e550d5bd4 100644
--- a/packages/core/src/api/api-result.ts
+++ b/packages/core/src/api/api-result.ts
@@ -1,5 +1,8 @@
+import type { ErrorDetails } from "../common/error.js";
+
 /** What every api handler returns: a rendered card, or a rendered error. */
 export interface ApiResult {
   status: "success" | "error - permanent" | "error - temporary";
+  error?: ErrorDetails;
   content: string;
 }
diff --git a/packages/core/src/api/gist.ts b/packages/core/src/api/gist.ts
index 75547d9ea08ea..0a4f05e9e1134 100644
--- a/packages/core/src/api/gist.ts
+++ b/packages/core/src/api/gist.ts
@@ -3,6 +3,7 @@ import type { ColorParams } from "../common/color.js";
 import { findInvalidColorParam, pickColorParams } from "../common/color.js";
 import {
   MissingParamError,
+  describeError,
   retrieveSecondaryMessage,
 } from "../common/error.js";
 import { parseBoolean } from "../common/ops.js";
@@ -103,6 +104,7 @@ export default async (
     if (err instanceof Error) {
       return {
         status: "error - temporary",
+        error: describeError(err),
         content: renderError({
           message: err.message,
           secondaryMessage: retrieveSecondaryMessage(err),
diff --git a/packages/core/src/api/index.js b/packages/core/src/api/index.js
index b7570b3280845..95a99eb0fdf50 100644
--- a/packages/core/src/api/index.js
+++ b/packages/core/src/api/index.js
@@ -2,6 +2,7 @@ import { renderStatsCard } from "../cards/stats.js";
 import { findInvalidColorParam, pickColorParams } from "../common/color.js";
 import {
   MissingParamError,
+  describeError,
   retrieveSecondaryMessage,
 } from "../common/error.js";
 import { parseArray, parseBoolean } from "../common/ops.js";
@@ -160,6 +161,7 @@ export default async (
     if (err instanceof Error) {
       return {
         status: "error - temporary",
+        error: describeError(err),
         content: renderError({
           message: err.message,
           secondaryMessage: retrieveSecondaryMessage(err),
diff --git a/packages/core/src/api/pin.js b/packages/core/src/api/pin.js
index 7d5688459369d..b584ccf26c11d 100644
--- a/packages/core/src/api/pin.js
+++ b/packages/core/src/api/pin.js
@@ -2,6 +2,7 @@ import { renderRepoCard } from "../cards/repo.js";
 import { findInvalidColorParam, pickColorParams } from "../common/color.js";
 import {
   MissingParamError,
+  describeError,
   retrieveSecondaryMessage,
 } from "../common/error.js";
 import { parseArray, parseBoolean } from "../common/ops.js";
@@ -105,6 +106,7 @@ export default async (
     if (err instanceof Error) {
       return {
         status: "error - temporary",
+        error: describeError(err),
         content: renderError({
           message: err.message,
           secondaryMessage: retrieveSecondaryMessage(err),
diff --git a/packages/core/src/api/top-langs.js b/packages/core/src/api/top-langs.js
index db3ba3141917c..74076bca2c4c2 100644
--- a/packages/core/src/api/top-langs.js
+++ b/packages/core/src/api/top-langs.js
@@ -2,6 +2,7 @@ import { renderTopLanguages } from "../cards/top-languages.js";
 import { findInvalidColorParam, pickColorParams } from "../common/color.js";
 import {
   MissingParamError,
+  describeError,
   retrieveSecondaryMessage,
 } from "../common/error.js";
 import { parseArray, parseBoolean } from "../common/ops.js";
@@ -132,6 +133,7 @@ export default async (
     if (err instanceof Error) {
       return {
         status: "error - temporary",
+        error: describeError(err),
         content: renderError({
           message: err.message,
           secondaryMessage: retrieveSecondaryMessage(err),
diff --git a/packages/core/src/api/wakatime.js b/packages/core/src/api/wakatime.js
index 56b2b457ab7e2..d2f143483d598 100644
--- a/packages/core/src/api/wakatime.js
+++ b/packages/core/src/api/wakatime.js
@@ -2,6 +2,7 @@ import { renderWakatimeCard } from "../cards/wakatime.js";
 import { findInvalidColorParam, pickColorParams } from "../common/color.js";
 import {
   MissingParamError,
+  describeError,
   retrieveSecondaryMessage,
 } from "../common/error.js";
 import { parseArray, parseBoolean } from "../common/ops.js";
@@ -90,6 +91,7 @@ export default async ({
     if (err instanceof Error) {
       return {
         status: "error - temporary",
+        error: describeError(err),
         content: renderError({
           message: err.message,
           secondaryMessage: retrieveSecondaryMessage(err),
diff --git a/packages/core/src/common/error.ts b/packages/core/src/common/error.ts
index 0cb3b0f8c5877..3c751586332e6 100644
--- a/packages/core/src/common/error.ts
+++ b/packages/core/src/common/error.ts
@@ -87,10 +87,45 @@ const retrieveSecondaryMessage = (err: Error): string | undefined => {
     : undefined;
 };
 
+/**
+ * Structured details of a caught error for API results.
+ */
+export interface ErrorDetails {
+  /** Error type such as `MAX_RETRY`. Absent when the error has no type. */
+  type?: string;
+  message: string;
+  secondaryMessage?: string;
+}
+
+/**
+ * Extract structured details from a caught error.
+ *
+ * Callers attach the result to API results as an optional `error` field.
+ * The `status` value itself stays stable, so exact comparisons in
+ * `apps/backend/router.js` and external callers keep working.
+ *
+ * @param err The caught error.
+ * @returns The available error details.
+ */
+const describeError = (err: Error): ErrorDetails => {
+  const details: ErrorDetails = { message: err.message };
+  const secondaryMessage = retrieveSecondaryMessage(err);
+
+  if (err instanceof CustomError) {
+    details.type = err.type;
+  }
+  if (secondaryMessage !== undefined) {
+    details.secondaryMessage = secondaryMessage;
+  }
+
+  return details;
+};
+
 export {
   CustomError,
   MissingParamError,
   SECONDARY_ERROR_MESSAGES,
   TRY_AGAIN_LATER,
+  describeError,
   retrieveSecondaryMessage,
 };
diff --git a/packages/core/tests/describeError.test.ts b/packages/core/tests/describeError.test.ts
new file mode 100644
index 0000000000000..3d9b82a8a9eb6
--- /dev/null
+++ b/packages/core/tests/describeError.test.ts
@@ -0,0 +1,107 @@
+import axios from "axios";
+import MockAdapter from "axios-mock-adapter";
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+
+import api from "../src/api/index.js";
+import {
+  CustomError,
+  MissingParamError,
+  describeError,
+} from "../src/common/error.js";
+
+vi.mock(import("../src/common/log.js"), async () => {
+  const { createLoggerMock } = await import("./utils.js");
+  return createLoggerMock();
+});
+
+// The handler is a JS function whose inferred options type spells out every
+// query parameter. Tests pass partial query maps on purpose and only assert
+// the parts of the result they care about, so they call through this
+// deliberately narrowed view instead of the raw inferred signature.
+interface TestApiResult {
+  status: string;
+  error?: {
+    type?: string;
+    message?: string;
+    secondaryMessage?: string;
+  };
+  content: string;
+}
+const callApi = (options: Record<string, unknown>): Promise<TestApiResult> => {
+  return api(options as Parameters<typeof api>[0]);
+};
+
+describe("Test describeError", () => {
+  it("should return message only for errors without a type", () => {
+    expect(describeError(new Error("boom"))).toStrictEqual({
+      message: "boom",
+    });
+  });
+
+  it("should return type and message for custom errors", () => {
+    expect(
+      describeError(
+        new CustomError(
+          "Downtime due to GitHub API rate limiting",
+          CustomError.MAX_RETRY,
+        ),
+      ),
+    ).toStrictEqual({
+      type: CustomError.MAX_RETRY,
+      message: "Downtime due to GitHub API rate limiting",
+      secondaryMessage:
+        "You can deploy own instance or wait until public will be no longer limited",
+    });
+  });
+
+  it("should omit the type for missing param errors", () => {
+    expect(describeError(new MissingParamError(["username"]))).toStrictEqual({
+      message:
+        'Missing params "username" make sure you pass the parameters in URL',
+    });
+  });
+
+  it("should return a secondary message when available", () => {
+    expect(
+      describeError(
+        new MissingParamError(["username"], "Specify a GitHub username"),
+      ),
+    ).toStrictEqual({
+      message:
+        'Missing params "username" make sure you pass the parameters in URL',
+      secondaryMessage: "Specify a GitHub username",
+    });
+  });
+});
+
+describe("Test API result error contract", () => {
+  let mock: MockAdapter;
+
+  beforeEach(() => {
+    mock = new MockAdapter(axios);
+  });
+
+  afterEach(() => {
+    mock.restore();
+  });
+
+  it("stats handler should keep status stable and attach typed details on rate limit exhaustion", async () => {
+    mock.onPost("https://api.github.com/graphql").reply(200, {
+      errors: [{ type: "RATE_LIMITED" }],
+    });
+
+    const result = await callApi({ username: "octocat" });
+
+    // status keeps its exact value for comparisons in apps/backend/router.js
+    expect(result.status).toBe("error - temporary");
+    expect(result).toMatchObject({
+      status: "error - temporary",
+      error: {
+        type: CustomError.MAX_RETRY,
+        message: "Downtime due to GitHub API rate limiting",
+        secondaryMessage:
+          "You can deploy own instance or wait until public will be no longer limited",
+      },
+    });
+  });
+});