---
name: api-contract-testing-128ad6cf0c3d
description: Verifies API contracts between services using consumer-driven contracts, schema validation, and tools like Pact. Use when testing microservices communication, preventing breaking changes, or validating OpenAPI specifications.
license: MIT
---

# API Contract Testing

Verify that APIs honor their contracts between consumers and providers without requiring full integration tests.

## Key Concepts

| Term | Definition |
|------|------------|
| Consumer | Service that calls an API |
| Provider | Service that exposes an API |
| Contract | Agreed request/response format |
| Pact | Consumer-driven contract testing tool |
| Schema | Structure definition (OpenAPI, JSON Schema) |
| Broker | Central repository for contracts |

## Pact Consumer Test (TypeScript)

```typescript
import { PactV3, MatchersV3 } from '@pact-foundation/pact';

const provider = new PactV3({
  consumer: 'OrderService',
  provider: 'UserService'
});

describe('User API Contract', () => {
  it('returns user by ID', async () => {
    await provider
      .given('user 123 exists')
      .uponReceiving('a request for user 123')
      .withRequest({ method: 'GET', path: '/users/123' })
      .willRespondWith({
        status: 200,
        body: MatchersV3.like({
          id: '123',
          name: MatchersV3.string('John'),
          email: MatchersV3.email('john@example.com')
        })
      })
      .executeTest(async (mockServer) => {
        const response = await fetch(`${mockServer.url}/users/123`);
        expect(response.status).toBe(200);
      });
  });

  it('returns 404 for non-existent user', async () => {
    await provider
      .given('user does not exist')
      .uponReceiving('a request for non-existent user')
      .withRequest({ method: 'GET', path: '/users/999' })
      .willRespondWith({
        status: 404,
        body: MatchersV3.like({
          error: { code: 'NOT_FOUND', message: MatchersV3.string() }
        })
      })
      .executeTest(async (mockServer) => {
        const response = await fetch(`${mockServer.url}/users/999`);
        expect(response.status).toBe(404);
      });
  });
});
```

## Provider Verification

```typescript
import { Verifier } from '@pact-foundation/pact';

new Verifier({
  provider: 'UserService',
  providerBaseUrl: 'http://localhost:3000',
  pactBrokerUrl: process.env.PACT_BROKER_URL,
  publishVerificationResult: true,
  providerVersion: process.env.GIT_SHA,
  stateHandlers: {
    'user 123 exists': async () => {
      await db.users.create({ id: '123', name: 'John' });
    },
    'user does not exist': async () => {
      await db.users.deleteAll();
    }
  }
}).verifyProvider();
```

## OpenAPI Validation (Express)

```javascript
const OpenApiValidator = require('express-openapi-validator');

app.use(OpenApiValidator.middleware({
  apiSpec: './openapi.yaml',
  validateRequests: true,
  validateResponses: true,
  validateSecurity: true
}));
```

## Additional Implementations

- **Python JSON Schema**: See [references/python-json-schema.md](references/python-json-schema.md)
- **Java REST Assured**: See [references/java-rest-assured.md](references/java-rest-assured.md)
- **Pact Broker CI/CD**: See [references/pact-broker-cicd.md](references/pact-broker-cicd.md)

## Best Practices

**Do:**
- Test from consumer perspective
- Use matchers for flexible matching
- Validate structure, not specific values
- Version contracts explicitly
- Test error responses
- Run tests in CI pipeline
- Test backward compatibility

**Don't:**
- Test business logic in contracts
- Hard-code specific values
- Skip error scenarios
- Ignore versioning
- Deploy without verification

## Tools

- **Pact** - Multi-language consumer-driven contracts
- **Spring Cloud Contract** - JVM ecosystem
- **OpenAPI/Swagger** - Schema-first validation
- **Dredd** - API blueprint testing
- **Spectral** - OpenAPI linting


---
Source attribution: secondsky
Original project: https://github.com/secondsky/claude-skills/blob/88378361314f558fb719aec0af9fd898ab36f0b2/plugins/api-contract-testing/skills/api-contract-testing/SKILL.md
License: MIT
License information: https://opensource.org/license/mit
Original upstream instructions; downloaded from Mega AI Hub.

## Upstream license notice

MIT License

Copyright (c) 2025 Claude Skills Maintainers

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.



# Mega AI Hub resource metadata

Creator / publisher: secondsky
Original project: https://github.com/secondsky/claude-skills/blob/88378361314f558fb719aec0af9fd898ab36f0b2/plugins/api-contract-testing/skills/api-contract-testing/SKILL.md
Attribution basis: Source repository record

Fields of work: Development & Engineering, Product Management
Roles: Backend Developer, Data Engineer, DevOps / SRE, Product Manager, QA / Test Engineer
Specialties: API, Backend, DevOps, Frontend, Git, Mobile, Testing
Tools: Openapivalidator, Pact
Country applicability: Country not specified
Classification basis: Source catalog labels
Instruction SHA-256: 68449db6c4f4c35a14b1702109f7e85cc55e7a1e6f3360d9450a7b8b54d3e158