@@ -0,0 +1,12 @@
+# PROD
+CRYSTALLIZE_TENANT_ID=your-tenant-id-here
+CRYSTALLIZE_TENANT_IDENTIFIER=your-tenant-identifier-here
+CRYSTALLIZE_ACCESS_TOKEN_ID=your-token-id-here
+CRYSTALLIZE_ACCESS_TOKEN_SECRET=your-token-secret-here
+
+# # DEV
+# CRYSTALLIZE_TENANT_ID=your-dev-tenant-id-here
+# CRYSTALLIZE_TENANT_IDENTIFIER=your-dev-tenant-identifier-here
+# CRYSTALLIZE_ACCESS_TOKEN_ID=your-dev-token-id-here
+# CRYSTALLIZE_ACCESS_TOKEN_SECRET=your-dev-token-secret-here
+# CRYSTALLIZE_ORIGIN=-dev.crystallize.digital
@@ -1,5 +1,6 @@
 node_modules/
 dist/
+.env
 
 yarn.lock
 package-lock.json
@@ -63,6 +63,8 @@ api.close();
     - `origin` custom host suffix (defaults to `.crystallize.com`)
 - options
     - `useHttp2` enable HTTP/2 transport
+    - `timeout` request timeout in milliseconds; requests that take longer will be aborted
+    - `http2IdleTimeout` HTTP/2 idle timeout in milliseconds (default `300000` — 5 minutes). Use a shorter value for serverless functions, a longer one for long-running servers
     - `profiling` callbacks
     - `extraHeaders` extra request headers for all calls
     - `shopApiToken` controls auto-fetch: `{ doNotFetch?: boolean; scopes?: string[]; expiresIn?: number }`
@@ -89,6 +91,23 @@ Pass the relevant credentials to `createClient`:
 
 See the official docs for auth: https://crystallize.com/learn/developer-guides/api-overview/authentication
 
+### Error handling
+
+API call errors throw a `JSApiClientCallError` with both `code` and `statusCode` properties for the HTTP status:
+
+```typescript
+import { JSApiClientCallError } from '@crystallize/js-api-client';
+
+try {
+    await api.pimApi(`query { … }`);
+} catch (e) {
+    if (e instanceof JSApiClientCallError) {
+        console.error(`HTTP ${e.statusCode}:`, e.message);
+        // e.code also works (same value)
+    }
+}
+```
+
 ## Profiling requests
 
 Log queries, timings and server timing if available.
@@ -378,7 +397,36 @@ const bulkKey = await files.uploadMassOperationFile('/absolute/path/to/import.zi
 
 [crystallizeobject]: crystallize_marketing|folder|625619f6615e162541535959
 
-## Mass Call Client
+## Mass Call Client (Deprecated)
+
+> **Deprecated:** Use mature ecosystem packages like [`p-limit`](https://www.npmjs.com/package/p-limit) or [`p-queue`](https://www.npmjs.com/package/p-queue) instead. They provide better error handling, TypeScript support, and are actively maintained.
+
+### Recommended alternative using p-limit
+
+```typescript
+import pLimit from 'p-limit';
+import { createClient } from '@crystallize/js-api-client';
+
+const api = createClient({ tenantIdentifier: 'my-tenant', accessTokenId: '…', accessTokenSecret: '…' });
+const limit = pLimit(5); // max 5 concurrent requests
+
+const mutations = items.map((item) =>
+    limit(() =>
+        api.pimApi(
+            `mutation UpdateItem($id: ID!, $name: String!) { product { update(id: $id, input: { name: $name }) { id } } }`,
+            { id: item.id, name: item.name },
+        ),
+    ),
+);
+
+const results = await Promise.allSettled(mutations);
+const failed = results.filter((r) => r.status === 'rejected');
+console.log(`Done: ${results.length - failed.length} succeeded, ${failed.length} failed`);
+```
+
+### Legacy usage
+
+The mass call client is still functional but will emit a deprecation warning on first use.
 
 Sometimes, when you have many calls to do, whether they are queries or mutations, you want to be able to manage them asynchronously. This is the purpose of the Mass Call Client. It will let you be asynchronous, managing the heavy lifting of lifecycle, retry, incremental increase or decrease of the pace, etc.
 
@@ -396,8 +444,7 @@ These are the main features:
 - Optional lifecycle function *afterRequest* (sync) to execute after each request. You also get the result in there, if needed
 
 ```javascript
-// import { createMassCallClient } from '@crystallize/js-api-client';
-const client = createMassCallClient(api, { initialSpawn: 1 }); // api created via createClient(...)
+const client = createMassCallClient(api, { initialSpawn: 1 });
 
 async function run() {
     for (let i = 1; i <= 54; i++) {
@@ -416,5 +463,3 @@ async function run() {
 }
 run();
 ```
-
-Full example: https://github.com/CrystallizeAPI/libraries/blob/main/components/js-api-client/src/examples/dump-tenant.ts
 
@@ -1,3 +1,29 @@
+# Upgrade Guide
+
+## From v5
+
+### `extraHeaders` type widened
+
+The `extraHeaders` option on `createClient` now accepts `Record<string, string> | Headers | [string, string][]` instead of only `Record<string, string>`. This is **not a breaking change** — all existing code continues to work. If you were casting headers to `Record<string, string>`, you can now pass `Headers` instances or tuple arrays directly.
+
+### HTTP/2 stability
+
+The HTTP/2 transport now guards against double-settlement of promises when abort signals fire after a request has already completed. No API changes — this is a reliability fix.
+
+### `JSApiClientCallError.statusCode` alias
+
+A read-only `statusCode` getter was added as an alias for `code`, following the Node.js convention. Both properties return the same numeric HTTP status.
+
+### `http2IdleTimeout` option
+
+You can now configure the HTTP/2 session idle timeout via `createClient(config, { http2IdleTimeout: 60000 })`. The default remains 300 000 ms (5 minutes).
+
+### `timeout` option
+
+A request-level timeout can be set via `createClient(config, { timeout: 10000 })`. When set, requests that exceed the timeout are aborted with an `AbortError`.
+
+---
+
 # Upgrade Guide to v5
 
 This guide helps you migrate from v4 to v5 of `@crystallize/js-api-client`.
 
@@ -1,7 +1,7 @@
 {
     "name": "@crystallize/js-api-client",
     "license": "MIT",
-    "version": "5.3.0",
+    "version": "6.0.0",
     "type": "module",
     "author": "Crystallize <hello@crystallize.com> (https://crystallize.com)",
     "contributors": [
@@ -26,20 +26,20 @@
     },
     "types": "./dist/index.d.ts",
     "main": "./dist/index.cjs",
-    "module": "./dist/index.mjs",
+    "module": "./dist/index.js",
     "devDependencies": {
-        "@tsconfig/node22": "^22.0.2",
-        "@types/node": "^24.2.0",
-        "dotenv": "^16.6.1",
-        "tsup": "^8.5.0",
-        "typescript": "^5.9.2",
-        "vitest": "^3.2.4"
+        "@tsconfig/node22": "^22.0.5",
+        "@types/node": "^25.5.2",
+        "dotenv": "^17.4.0",
+        "tsup": "^8.5.1",
+        "typescript": "^6.0.2",
+        "vitest": "^4.1.2"
     },
     "dependencies": {
         "@crystallize/schema": "workspace:*",
         "json-to-graphql-query": "^2.3.0",
         "mime-lite": "^1.0.3",
-        "zod": "^4.1.12"
+        "zod": "^4.3.6"
     },
     "browser": {
         "fs": false,
 
@@ -22,6 +22,25 @@ export type CatalogueFetcherGrapqhqlOnFolder<OC = unknown> = {
     onChildren?: OC;
 };
 
+/**
+ * Creates a catalogue fetcher that executes queries against the Crystallize Catalogue API using JSON-based query objects.
+ * Use this when you want to build catalogue queries programmatically instead of writing raw GraphQL strings.
+ *
+ * @param client - A Crystallize client instance created via `createClient`.
+ * @returns A function that accepts a JSON query object and optional variables, and returns the catalogue data.
+ *
+ * @example
+ * ```ts
+ * const fetcher = createCatalogueFetcher(client);
+ * const data = await fetcher({
+ *   catalogue: {
+ *     __args: { path: '/my-product', language: 'en' },
+ *     name: true,
+ *     path: true,
+ *   },
+ * });
+ * ```
+ */
 export const createCatalogueFetcher = (client: ClientInterface) => {
     return <T = unknown>(query: object, variables?: VariablesType): Promise<T> => {
         return client.catalogueApi<T>(jsonToGraphQLQuery({ query }), variables);
@@ -64,7 +83,7 @@ function onFolder<OF = unknown>(onFolder?: OF, c?: CatalogueFetcherGrapqhqlOnFol
     const children = () => {
         if (c?.onChildren) {
             return {
-                chidlren: {
+                children: {
                     ...c.onChildren,
                 },
             };
 
@@ -112,6 +112,20 @@ function buildNestedNavigationQuery(
     return jsonToGraphQLQuery({ query });
 }
 
+/**
+ * Creates a navigation fetcher that builds nested tree queries for folder-based or topic-based navigation.
+ * Use this to retrieve hierarchical navigation structures from the Crystallize catalogue.
+ *
+ * @param client - A Crystallize client instance created via `createClient`.
+ * @returns An object with `byFolders` and `byTopics` methods for fetching navigation trees at a given depth.
+ *
+ * @example
+ * ```ts
+ * const nav = createNavigationFetcher(client);
+ * const folderTree = await nav.byFolders('/', 'en', 3);
+ * const topicTree = await nav.byTopics('/', 'en', 2);
+ * ```
+ */
 export function createNavigationFetcher(client: ClientInterface): {
     byFolders: TreeFetcher;
     byTopics: TreeFetcher;
 
@@ -87,7 +87,7 @@ function byPaths(client: ClientInterface, options?: ProductHydraterOptions): Pro
         }, {} as any);
 
         const query = {
-            ...{ ...productListQuery },
+            ...productListQuery,
             ...(extraQuery !== undefined ? extraQuery : {}),
         };
 
@@ -140,6 +140,21 @@ function bySkus(client: ClientInterface, options?: ProductHydraterOptions): Prod
     };
 }
 
+/**
+ * Creates a product hydrater that fetches full product data from the catalogue by paths or SKUs.
+ * Use this to enrich a list of product references with complete variant, pricing, and attribute data.
+ *
+ * @param client - A Crystallize client instance created via `createClient`.
+ * @param options - Optional settings for market identifiers, price lists, and price-for-everyone inclusion.
+ * @returns An object with `byPaths` and `bySkus` methods for hydrating products.
+ *
+ * @example
+ * ```ts
+ * const hydrater = createProductHydrater(client);
+ * const products = await hydrater.byPaths(['/shop/my-product'], 'en');
+ * const productsBySkus = await hydrater.bySkus(['SKU-001', 'SKU-002'], 'en');
+ * ```
+ */
 export function createProductHydrater(client: ClientInterface, options?: ProductHydraterOptions) {
     return {
         byPaths: byPaths(client, options),