yuhuabillchen/justfit-mlx/server-inference

Server Inference

Use this workflow for the FastAPI server and API-compatible inference.

First Checks

1. Identify the server command, model, port, request endpoint, request body, and expected response.
2. Start with health/model-list checks before debugging generation.
3. Separate server startup failures from request-handling failures.
4. Keep streaming and non-streaming repros separate.

Startup

uv run mlx_vlm.server \
  --model <model-or-path> \
  --port 8080

Useful startup flags include --adapter-path, --trust-remote-code, --log-level, --enable-thinking, --thinking-budget, --draft-model, --draft-kind, --kv-bits, --kv-quant-scheme, --max-kv-size, and --vision-cache-size.

Minimal Checks

curl http://127.0.0.1:8080/health
curl http://127.0.0.1:8080/v1/models
curl http://127.0.0.1:8080/metrics

Minimal chat request:

curl -s http://127.0.0.1:8080/v1/chat/completions \
  -H 'Content-Type: application/json' \
  -d '{
    "model": "<model-or-path>",
    "messages": [{"role": "user", "content": "Say hello."}],
    "max_tokens": 32,
    "stream": false
  }'

Minimal Responses API request:

curl -s http://127.0.0.1:8080/v1/responses \
  -H 'Content-Type: application/json' \
  -d '{
    "model": "<model-or-path>",
    "input": "Say hello.",
    "max_output_tokens": 32
  }'

Endpoint Surface (beyond chat/responses)

The server exposes more than chat — cover or route to these as needed:

• Anthropic Messages API: /v1/messages, plus /v1/messages/count for token counting.
• Audio: /v1/audio/speech (TTS), /v1/audio/transcriptions and /v1/audio/translations (STT).
• Images: /v1/images/generations and /v1/images/edits (diffusion image models).
• Cache & metrics: /v1/cache/stats, /v1/cache/reset, /v1/metrics.
• Models: /v1/models lists models loaded by this process by default. Use --model-discovery hf-cache for shared Hugging Face cache discovery — see Skill("mlx-vlm-skills:hf-cache-models").

Match the model kind to the endpoint (an image endpoint needs a diffusion/image model, audio endpoints need an audio model); a mismatch returns a clear 4xx, not a crash.

Debugging Rules

• Capture the server command, server logs, request body, response status, and response body.
• Test /v1/models after preload/load changes.
• For OpenAI client issues, reproduce with curl before blaming the client SDK.
• For streaming bugs, save raw event chunks and compare with non-streaming.
• For structured outputs, isolate the JSON schema and confirm whether the same request works without schema constraints.
• For tool calls, inspect native support and the parser inferred from the loaded processor's actual chat template. Follow Tool Calling for parser registration and validation.

Validation

• For route/schema changes, run uv run pytest mlx_vlm/tests/test_server.py -q.
• For structured output changes, include uv run pytest mlx_vlm/tests/test_structured.py -q.
• For tool parser changes, add compact regressions to TestProcessToolCalls in mlx_vlm/tests/test_server.py and run the shared streaming tests in test_responses_state.py, plus any existing tests for affected parsers. Reuse consolidated tests instead of creating a new test file.
• If the result is a user-facing bug report, switch to Skill("mlx-vlm-skills:reproducible-github-issues").