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API Mock & Contract Builder
The problem Frontend and mobile developers are constantly blocked by missing or unstable backend endpoints during the build phase.
$16
API Mock & Contract Builder
Example session with this skill installed
Analyze my InventoryTable.tsx component and generate an OpenAPI 3.1 spec, Zod schemas, and an Express.js mock server for managing warehouse stock levels.
- Read your context and instructions
- Compiled the api mock
Analyzed InventoryTable.tsx. Generated OpenAPI 3.1 specification, Zod validation schemas, and a functional Express.js mock server with 10 realistic stock records.
API Mock & Contract Implementation
# openapi.yaml
openapi: 3.1.0
info:
title: Inventory Management API
version: 1.0.0
paths:
/api/v1/inventory:
get:
summary: List inventory items
parameters:
- name: limit
in: query
schema:
type: integer
default: 10
responses:
'200':
description: A list of inventory items
content:
application/json:
schema:
$ref: '#/components/schemas/InventoryPage'
components:
schemas:
InventoryItem:
type: object
required: [id, sku, quantity, status]
properties:
id: { type: string, format: uuid }
sku: { type: string, pattern: '^[A-Z]{3}-\\d{4}$' }
quantity: { type: integer, minimum: 0 }
status: { type: string, enum: [IN_STOCK, LOW_STOCK, OUT_OF_STOCK] }
InventoryPage:
type: object
properties:
items:
type: array
items: { $ref: '#/components/schemas/InventoryItem' }
total: { type: integer }
// schemas.ts
import { z } from 'zod';
export const InventoryItemSchema = z.object({
id: z.string().uuid(),
sku: z.string().regex(/^[A-Z]{3}-\d{4}$/),
quantity: z.number().min(0),
status: z.enum(['IN_STOCK', 'LOW_STOCK', 'OUT_OF_STOCK']),
});
export type InventoryItem = z.infer<typeof InventoryItemSchema>;
// mock-server.js
// Dependencies: express, uuid
const express = require('express');
const app = express();
const PORT = 4000;
const inventory = [
{ id: '550e8400-e29b-41d4-a716-446655440000', sku: 'WHS-1024', quantity: 45, status: 'IN_STOCK' },
{ id: '7c9e6679-7425-40de-944b-e07fc1f90ae7', sku: 'WHS-2055', quantity: 2, status: 'LOW_STOCK' }
];
app.get('/api/v1/inventory', (req, res) => {
setTimeout(() => {
res.json({ items: inventory, total: inventory.length });
}, 250); // Simulated latency
});
app.listen(PORT, () => console.log(`Mock server running on port ${PORT}`));
Next steps
- Run
npm install express uuidto install the mock server dependencies. - Verify the
skuregex pattern matches your specific warehouse naming conventions. - Integrate the
InventoryItemtype into your React component's data fetching hook.
Connects securely to your tools. The creator never sees your data.
What you get
About this skill
The problem
Frontend and mobile developers are constantly blocked by missing or unstable backend endpoints during the build phase. Relying on manual, hard-coded mock objects leads to drift between the UI and the actual production API, causing breaking changes at integration.
What it does
- Generates strict OpenAPI 3.1.0 JSON and YAML specifications with reusable domain models.
- Constructs drop-in mock handlers for MSW (v2), Express.js, or FastAPI with simulated network latency.
- Synthesizes realistic relational seed datasets using valid UUIDs, ISO timestamps, and industry-specific strings.
- Produces synchronized Zod (TypeScript) and Pydantic v2 (Python) validation schemas to ensure type safety.
- Validates generated contracts against industry-standard linters and smoke-tests mock endpoints before delivery.
Frameworks & tools
OpenAPI 3.1, TypeScript, Zod, Python, Pydantic v2, MSW (Mock Service Worker), Express.js, FastAPI, and Vitest/Pytest for smoke testing.
Why this beats prompting it yourself
General LLMs often produce hallucinated OpenAPI fields or inconsistent types between the spec and the mock implementation. This skill enforces strict RFC 7807 error patterns, consistent pagination paradigms, and performs internal compilation checks to ensure the generated code actually runs without manual fixes.
Use cases
- Unblock frontend development before the backend team has finished the API implementation.
- Generate comprehensive integration test suites with realistic, randomized seed data.
- Deduce API requirements directly from existing React/Vue components to document legacy systems.
- Test frontend resilience by simulating high-latency or specific HTTP error states (422, 401).
Known limitations
Requires local installation of runtime packages like msw, express, or fastapi as specified in the output. Inference from UI components treats ambiguous fields as proposals requiring user confirmation.
How to install
Works the same in every agent - Claude, Cursor, Codex, Copilot and 20+ more.
- 1
Download the ZIP
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- 2
Unzip into your skills folder
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- 3
Ask your agent to use it
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Verified clean 23 days ago
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