Open Source · Cross Platform · Any Tech Stack
Test beyond
the happy path.
Dev Proxy is an API simulator that helps you test how your app handles errors, throttling, and slow responses — without changing a single line of code.
❯ devproxy
info Dev Proxy listening on 127.0.0.1:8000...
req GET https://api.contoso.com/posts
skip GenericRandomErrorPlugin: Pass through
pass Passed through
req GET https://api.contoso.com/posts
skip RetryAfterPlugin: Request not throttled
oops GenericRandomErrorPlugin: 429 429
You test the happy path.
Your users get the rest.
APIs fail. They throttle. They respond slowly. They return unexpected data. And when they do, your app needs to handle it gracefully. But simulating these failures is hard — until now.
API Mocking
Mock APIs that don't exist yet.
Stand up a fully-functional CRUD API without writing a single line of server code. Design, prototype, and build your frontend in parallel with your backend.
Learn more →// customers-api.json — CrudApiPlugin
"baseUrl": "https://api.contoso.com/customers"
getAll GET /customers
getOne GET /customers/{id}
create POST /customers
merge PATCH /customers/{id}
delete DELETE /customers/{id}
// Defined in JSON. Zero server code.
Resilience Testing
See how your app handles API errors.
Simulate random errors, timeouts, and failures for any API — without touching your code. Build more robust apps and never lose your customers' data.
Learn more →// errors-contoso-api.json
"url": "https://api.contoso.com/*"
"responses":
500 Internal Server Error
429 Too Many Requests
503 Service Unavailable
// Random errors at configured failure rate.
AI / LLM Testing
Build & test AI apps without burning tokens.
Route OpenAI and Azure OpenAI API calls to a local language model during development. Get real responses while building your AI-powered apps — without spending tokens.
Learn more →// Your app calls OpenAI
POST /v1/chat/completions
// Dev Proxy routes to local LLM
→ Ollama (llama3.2)
200 { "choices": [{ "message": ... }] }
// Real responses. Zero API costs.
Rate Limit Simulation
Verify your app respects API limits.
Simulate rate limiting and throttling responses before they happen in production. Avoid getting blocked and deliver a smoother experience for your users.
Learn more →RateLimit-Limit: 3
Retry-After: 30
CI/CD Integration
Automate chaos testing in your pipeline.
Run Dev Proxy as part of your CI/CD pipeline to catch API integration issues before they reach production. Works with GitHub Actions, Azure DevOps, and more.
Learn more →# .github/workflows/test.yml
steps:
- name: Setup Dev Proxy
uses: dev-proxy-tools/actions/setup@v1
- name: Run tests
run: npm test
- name: Stop Dev Proxy
uses: dev-proxy-tools/actions/stop@v1
✓ 42 passed, 0 failed
Platform Agnostic
Works with everything you use.
Dev Proxy intercepts network traffic at the system level. It works with any language, framework, and API — no SDKs, no adapters, no code changes.
.NET
Node.js
Python
Java
React
Angular
Browser
Any REST API
How does your app handle
API errors?
Find out in minutes. Dev Proxy is open source and free.