Free Mock LLM API - Test and Develop AI Integrations Without Costs
Create free mock LLM streaming APIs for OpenAI, Anthropic Claude, and other AI providers. Perfect for developers testing AI features without burning through expensive API credits. No signup required.
How it works
Generate & configure
Get a unique endpoint automatically, then choose your LLM provider (OpenAI, Anthropic, Generic), content mode, and token generation settings
Use in development
Replace the baseURL in your SDK (OpenAI, Anthropic) to point to your mock endpoint. Build your UI, test streaming responses, and iterate without API costs
Use in testing
Run automated tests against your mock endpoint with predictable responses. Test error handling, edge cases, and CI/CD pipelines without draining your API budget
Why mock LLM APIs?
Save money
Develop and test AI features without spending thousands on API calls. Each OpenAI/Claude API call costs money - our mocks are completely free.
Instant testing
No API keys, no rate limits, no waiting. Test your streaming UI, error handling, and edge cases immediately.
Multiple provider support
Compatible with OpenAI ChatGPT/GPT-4, Anthropic Claude, and generic streaming formats. Switch providers without changing your code.
100% free
No trial periods, no credit card, no premium tiers. Unlimited mock API calls at zero cost.
Perfect for
- AI chatbot development: Build and perfect your chat UI before connecting to production LLM APIs
- Cost-effective testing: Test streaming behavior, error handling, and edge cases without API costs
- Learning AI integration: Practice implementing LLM features without expensive API subscriptions
- CI/CD pipelines: Run automated tests against LLM endpoints without draining your API budget
- Rapid prototyping: Demonstrate AI features to stakeholders before committing to paid APIs
- SDK development: Build and test AI SDKs and libraries with predictable mock responses
LLM mock features
No signup required
Start mocking LLM APIs immediately - zero friction
OpenAI & Anthropic formats
Full compatibility with OpenAI's streaming format (ChatGPT, GPT-4) and Anthropic's Claude API format with proper SSE response structures
Generic streaming
Standard SSE streaming format compatible with any LLM provider
Customizable & deterministic
Configure content modes (generated text, lorem ipsum, custom), token ranges, and latency. Get predictable, consistent responses perfect for performance benchmarking and reliable test baselines
Failover testing
Simulate provider outages and test failover logic between OpenAI, Claude, or custom providers without real downtime
REST API support
Need standard REST mocks too? Switch to the JSON Response tab for traditional API mocking
Common use cases
Building AI chatbots
Develop your entire chatbot interface and streaming logic without spending a dime on OpenAI or Anthropic credits during development.
Testing AI features
Validate your LLM integration, error handling, and UI responsiveness with predictable mock responses before production.
Developer training
Teach AI integration patterns without requiring students to sign up for paid API services or manage API keys.
Automated testing
Run comprehensive CI/CD tests against LLM endpoints without accumulating massive API bills from test runs.
Frequently Asked Questions
How much money can I save?
Significant amounts! OpenAI GPT-4 costs $0.03-0.06 per 1K tokens. During development, you might make thousands of test calls. With MockAPI Dog, all testing is free - save your budget for production.
Do the mocks work with OpenAI SDK?
Yes! Our OpenAI-format mocks are fully compatible with the official OpenAI SDK. Just point the baseURL to our endpoint and you're ready to go.
What about Anthropic Claude?
We support Anthropic's Claude API format including streaming. Perfect for testing Claude integrations without using your Anthropic credits.
Can I test streaming responses?
Absolutely. Our mocks support server-sent events (SSE) streaming just like real LLM providers. Test your streaming UI with realistic token-by-token delivery.
Is this only for LLM mocking?
No! MockAPI Dog also supports traditional REST API mocking with JSON responses. Switch to the 'JSON Response' tab on the homepage for REST API features.
Are there any usage limits?
No limits on the number of mock endpoints you create or API calls you make. Completely free and unlimited for all users.
Start mocking LLMs now
Stop wasting money on development and testing. MockAPI Dog's LLM mocking lets you build, test, and perfect your AI features completely free. Save your API budget for production.
No signup. No costs. Just build.