Start with LLM mocking. Add MCP, A2A, vector, and more when you need them. The aimock suite grows with your stack.
npx -p @copilotkit/aimock llmock -f ./fixtures
docker run -v $(pwd)/fixtures:/fixtures -p 4010:4010 ghcr.io/copilotkit/aimock -h 0.0.0.0 -f /fixtures
Or install as a library: npm install @copilotkit/aimock
{ "match": { "userMessage": "Hello" }, "response": { "content": "Hi there! How can I help?" }, "opts": { "chunkSize": 10, "latency": 1000 } }
Proxy unmatched requests to real APIs and capture every response.
Fixtures written to disk automatically as clean, editable JSON.
Deterministic responses in CI, forever. No API keys, no flakiness.
$ npx -p @copilotkit/aimock llmock --record --provider-openai https://api.openai.com ⚡ Listening on http://localhost:4010 ⚠ NO FIXTURE MATCH — proxying to https://api.openai.com/v1/chat/completions ✓ Recorded → fixtures/recorded/openai-2026-03-31T22:15:00.json ⚡ Fixture match — replaying from disk
One JSON config. One port. Every service your AI app depends on.
{ "llm": { "fixtures": "./fixtures/llm", "providers": ["openai", "claude", "gemini"] }, "mcp": { "tools": "./fixtures/mcp/tools.json", "resources": "./fixtures/mcp/resources.json" }, "a2a": { "agents": "./fixtures/a2a/agents.json" }, "vector": { "provider": "pinecone", "fixtures": "./fixtures/vector" } }
$ npx @copilotkit/aimock --config aimock.json ⚡ aimock v1.16.0 ✓ LLM mounted at /v1/chat/completions ✓ LLM mounted at /v1/messages ✓ LLM mounted at /v1/embeddings ✓ MCP mounted at /mcp/tools/* ✓ A2A mounted at /a2a/agents/* ✓ Vector mounted at /vectors/* ⚡ Listening on http://localhost:4010 6 services · 24 fixtures loaded
OpenAI, Claude, Gemini, Gemini Interactions, Bedrock, Azure, Vertex AI, Ollama, Cohere, ElevenLabs — full streaming and embeddings support for every provider.
Mock tools, resources, and prompts with full session management. Test your MCP integrations without running real tool servers.
Agent cards, message routing, and SSE streaming. Mock multi-agent interactions with deterministic responses.
Mock agent-to-UI event streams for CopilotKit frontend testing.
Pinecone, Qdrant, and ChromaDB compatible. Mock similarity search, upserts, and index operations with fixtures.
Drop, malformed, or disconnect at any probability. Verify your app gracefully handles every failure mode.
Image generation and editing, text-to-speech (OpenAI + ElevenLabs), audio transcription and translation, non-speech audio generation, and video generation — mock every multimedia endpoint with fixtures.
Zero-config useAimock() with auto server lifecycle, env var patching, and
match count reset.
Fixtures stay accurate as providers evolve. Fixes ship before your tests break.
LLM providers change their response formats without warning. aimock catches it within 24 hours and ships the fix before your tests break.
Daily CI hits actual OpenAI, Anthropic, Gemini endpoints to detect response format changes.
Response schemas are validated against aimock's builders. Any drift is flagged automatically.
Drift detected → fixtures, builders, skills, and docs updated → PR shipped. Always current, within a day.
| Capability | aimock | MSW | VidaiMock | mock-llm | piyook/llm-mock | mokksy/ai-mocks |
|---|---|---|---|---|---|---|
| Cross-process interception | Real server ✓ | In-process only | ✓ | ✓ (Docker) | ✓ | ✓ (Ktor) |
| Chat Completions SSE | Built-in ✓ | manual | ✓ | ✓ | ✓ | ✓ |
| Responses API SSE | Built-in ✓ | manual | ✓ | ✓ | ✓ | ✓ |
| Claude Messages API | Built-in ✓ | manual | ✓ | ✗ | ✓ | ✓ |
| Gemini streaming | Built-in ✓ | manual | ✓ | ✗ | ✓ | ✓ |
| Multi-provider support | 14 providers ✓ | manual | 12 providers | OpenAI only | OpenAI only | 5 providers |
| WebSocket APIs | Built-in ✓ | ✗ | ✗ | ✗ | ✗ | ✗ |
| Embeddings API | Built-in ✓ | ✗ | ✓ | ✗ | ✓ | ✓ |
| Image generation | Built-in ✓ | ✗ | ✓ | ✗ | ✗ | ✗ |
| Image editing | Built-in ✓ | ✗ | ✗ | ✗ | ✗ | ✗ |
| Text-to-Speech | Built-in ✓ | ✗ | ✗ | ✗ | ✗ | ✗ |
| Audio transcription | Built-in ✓ | ✗ | ✗ | ✗ | ✗ | ✗ |
| Audio translation | Built-in ✓ | ✗ | ✗ | ✗ | ✗ | ✗ |
| Non-speech audio | Built-in ✓ | ✗ | ✗ | ✗ | ✗ | ✗ |
| Video generation | Built-in ✓ | ✗ | ✗ | ✗ | ✗ | ✗ |
| AG-UI event mocking | Built-in ✓ | ✗ | ✗ | ✗ | ✗ | ✗ |
| MCP tool mocking | Built-in ✓ | ✗ | ✗ | ✗ | ✗ | ✗ |
| A2A agent mocking | Built-in ✓ | ✗ | ✗ | ✗ | ✗ | ✓ |
| Vector DB mocking | Built-in ✓ | ✗ | ✗ | ✗ | ✗ | ✗ |
| Search & rerank | Built-in ✓ | ✗ | ✗ | ✗ | ✗ | ✗ |
| Record & replay | Built-in ✓ | ✗ | ✗ | ✗ | ✗ | ✗ |
| Drift detection | ✓ | ✗ | ✗ | ✗ | ✗ | ✗ |
| Sequential / stateful responses | Built-in ✓ | manual | ✓ | ✓ | ✗ | ✗ |
| Request journal | ✓ | manual | ✓ | ✗ | ✓ | ✗ |
| Error injection | ✓ | ✓ | partial | ✗ | ✗ | ✗ |
| Chaos testing | Built-in ✓ | ✗ | ✓ | ✗ | ✗ | ✗ |
| Streaming physics | Built-in ✓ | ✗ | ✓ | ✗ | ✗ | ✗ |
| Structured output / JSON mode | Built-in ✓ | manual | ✓ | ✗ | ✗ | ✗ |
| Programmatic API | ✓ (TypeScript/JS) | ✓ (TypeScript/JS) | No (binary only) | ✗ | ✗ | ✓ (Kotlin/JVM) |
| Fixture files | JSON ✓ | Code-only | Tera templates | YAML config | JSON templates | ✗ |
| GitHub Action | Built-in ✓ | ✗ | ✗ | ✗ | ✓ | ✓ |
| Vitest / Jest plugins | Built-in ✓ | ✗ | ✗ | ✗ | ✗ | ✗ |
| Docker + Helm | Both ✓ | ✗ | Docker only | ✓ (Both) | Docker only | ✗ |
| Prometheus metrics | Built-in ✓ | ✗ | ✓ | ✗ | ✗ | ✗ |
| Streaming usage chunks | Built-in ✓ | ✗ | ✗ | ✗ | ✗ | ✗ |
| Rate limiting headers | Built-in ✓ | ✗ | ✗ | ✗ | ✗ | ✗ |
| Dependencies | Zero ✓ | ~300KB | Zero (Rust) | Node+Express | Minimal | JVM (Kotlin) |
AG-UI uses aimock for its end-to-end test suite, verifying AI agent behavior across LLM providers with fixture-driven responses in the codebase. Browse the example fixtures to get started.
MSW