mlx-mcp-server

A Model Context Protocol (MCP) server that gives Claude Code and Claude Desktop a set of tools to talk to a locally-running LLM. Optimised for oMLX and MLX LM on Apple Silicon, with support for any OpenAI-compatible backend (Ollama, LM Studio, etc.).

The idea: Claude stays Claude. Your local model becomes a tool Claude can call — fast, private, free, and clearly labelled 🏠 LOCAL in every response.

---

How it works

You (in Claude Code or Claude Desktop)
        │
        ▼
  Claude (Sonnet / your tier)          ← still the primary AI
        │
        │  calls MCP tools when useful
        ▼
  mlx-mcp-server  (subprocess)         ← this repo
        │
        │  HTTP  POST /v1/chat/completions
        ▼
  Your local LLM backend               ← oMLX · MLX LM · Ollama · LM Studio
        │
        ▼
  Response with 🏠 LOCAL badge         ← so you always know which model answered

Claude Code spawns mlx-mcp-server as a background subprocess at startup. The server sits idle until you — or Claude — explicitly invoke one of its tools. Nothing is routed automatically; you're always talking to real Claude unless a tool is called.

---

Quick install

macOS with Homebrew Python — use uv (pip is blocked by PEP 668):

uv tool install mlx-mcp-server

Other environments:

pip install mlx-mcp-server

oMLX (recommended on Apple Silicon)

# Add to Claude Code
mlx-mcp-server install --claude-code \
  --base-url http://localhost:8000 \
  --api-key YOUR_OMLX_KEY \
  --model "Qwen3-Coder-30B-A3B-Instruct-MLX-4bit"

# Add to Claude Desktop
mlx-mcp-server install \
  --base-url http://localhost:8000 \
  --api-key YOUR_OMLX_KEY \
  --model "Qwen3-Coder-30B-A3B-Instruct-MLX-4bit"

Also install the slash commands and helper scripts in one shot:

mlx-mcp-server install --claude-code \
  --base-url http://localhost:8000 \
  --api-key YOUR_OMLX_KEY \
  --model "Qwen3-Coder-30B-A3B-Instruct-MLX-4bit" \
  --full

MLX LM

# Start the server first
mlx_lm.server --model mlx-community/Qwen2.5-Coder-14B-Instruct-4bit

# Then install (no API key needed, model auto-detected)
mlx-mcp-server install --claude-code --base-url http://localhost:8080

Ollama

ollama serve && ollama pull qwen2.5-coder:14b

mlx-mcp-server install --claude-code \
  --base-url http://localhost:11434 \
  --model qwen2.5-coder:14b

Restart Claude Code / Claude Desktop after installing.

---

Tested model lineup (Apple Silicon)

These models were live-tested on an M5 MacBook Pro (32 GB) and benchmarked with quick_test code_review. All speeds are measured — not estimated from spec sheets.

Tier	Model	RAM	tok/s	Best for
⚡ Turbo	DeepSeek-Coder-V2-Lite-Instruct-4bit-mlx	~8 GB	~135	Quick lookups, boilerplate, instant subagent calls
⚡ Fast	Qwen2.5-Coder-7B-Instruct-4bit	~5 GB	~80	Speed fallback, lightweight code tasks
⚖️ Everyday	Qwen2.5-Coder-14B-Instruct-4bit	~9 GB	~28	Reliable everyday coding, code review
🧠 Default	Qwen3-Coder-30B-A3B-Instruct-MLX-4bit	~18 GB	~51	Best quality and the shipped default — MoE (3B active params), no thinking mode

The quality tier runs at ~51 tok/s despite 30B parameters because it's a Mixture of Experts model — only ~3B parameters are active per token. It fits in 18 GB and doesn't activate a thinking chain, making it ideal for subagent use.

As of v0.2.4 the 30B-A3B is the shipped default. A 24-case gated eval across six task categories (see reports below) found it passes everything at ~0.6 s median latency — as fast as the turbo tier — so there's no reason to default to a smaller model and escalate. The earlier multi-model "warm pool" scaffolding was dropped: the MoE makes the big model cheap enough to simply be the default.

---

Model research & findings

During development, several models were evaluated. Here's what was tested and why each was accepted or rejected.

Accepted

Model	Verdict	Notes
DeepSeek-Coder-V2-Lite-Instruct-4bit-mlx	✅ Kept	~135 tok/s on M5/32GB. Fastest option — unmatched for quick lookups and boilerplate.
Qwen2.5-Coder-7B-Instruct-4bit	✅ Kept	~80 tok/s. Speed fallback — dominates when 14B is too slow and turbo is overkill.
Qwen2.5-Coder-14B-Instruct-4bit	✅ Kept	~28 tok/s. Reliable everyday default. No non-thinking upgrade path exists at this size as of June 2026 (Qwen3-Coder goes no smaller than 30B-A3B).
Qwen3-Coder-30B-A3B-Instruct-MLX-4bit	✅ Kept	~51 tok/s. Best quality. MoE architecture means 30B params but only ~3B active per token. Clean output — no thinking chain.

Rejected

Model	Verdict	Reason
Qwen2.5-Coder-32B-Instruct-4bit	❌ Dropped	Strictly dominated by Qwen3-Coder-30B-A3B: slower (~19 tok/s vs ~51), older generation, same RAM footprint.
Qwen3-Coder-30B-A3B-Instruct-MLX-6bit	❌ Dropped	24.26 GB — too tight for 32 GB system even with Big Model Mode. Can't load reliably.
Qwen3.6-35B-A3B-Instruct-4bit	❌ Dropped	Thinking model — burns 2,100+ tokens on internal reasoning before every answer. Measured 39 seconds for a 3-sentence code review. Unusable as a subagent.
Gemma 4 31B (5-bit)	❌ Dropped	Two blockers: (1) oMLX rejects enable_thinking field → 400 Bad Request (fixed in client); (2) tokenizer.chat_template is not set — fundamental oMLX incompatibility, not fixable client-side.
Gemma 3 27B QAT 4bit	❌ Dropped	Measured ~7.5 tok/s on M5/32GB (not the ~35 tok/s seen in some benchmarks). Strictly dominated by Qwen3-Coder-30B-A3B on every axis: 7× slower, same RAM, same quality tier.

Key findings

• MoE models beat dense models at the quality tier. Qwen3-Coder-30B-A3B at 51 tok/s is faster than Qwen2.5-Coder-32B at 19 tok/s, with better quality. Active params (not total params) determine speed.
• Avoid thinking models for subagent use. Qwen3.6-35B-A3B and other /think-default models spend thousands of tokens reasoning before outputting a single word. Claude already handles the reasoning — your local model just needs to answer.
• Benchmark on your hardware. Published tok/s numbers for Gemma 3 27B QAT diverged significantly from measured M5/32GB performance. Always verify with quick_test before committing to a model.
• enable_thinking payload safety. The client only sends enable_thinking: true when explicitly requested. Sending enable_thinking: false unconditionally causes 400 errors on models that don't recognise the field (e.g., Gemma 4). See #1559 for the DFlash speculative decoding issue that routes Gemma 4 output to reasoning_content.
• On bounded work, speed is the differentiator — not quality. The gated eval harness (python -m mlx_mcp_server.eval run) found every coding model passes nearly all easy/medium cases; they separate on latency. The MoE 30B-A3B wins by being top-quality and turbo-fast. (Harder cases that separate models on quality are what the Phase-2 capture loop is for.)
• You can't sweep all models in one engine pool. Loading the small models first fills the ~24.5 GB pool, so the big ones then return 507 Insufficient Storage. Evaluate big models in isolation (one ~17 GB model at a time). This warm-pool/eviction limit is a hard constraint for any future auto-ladder selector.

Design & eval reports

Research notes and measured results captured during development (open in a browser):

• docs/eval-results-report.html — full 5-model gated eval: pass-rate, latency, and tokens per task category, with the ladder recommendation.
• docs/task-aware-routing-brainstorm.html — routing design v1: cascade vs. pre-route under a memory ceiling.
• docs/task-aware-routing-brainstorm-v2.html — v2: the warm-pool reframe and the single-GPU parallelism reality check.
• docs/task-aware-routing-brainstorm-v3.html — v3: GLM-5.2 won't fit 24 GB; Self-MoA shows weak-model councils underperform; best-of-N with the gate as verifier.

---

Tools

These are the MCP tools Claude can call. You can invoke them directly by name in conversation, or ask Claude to use the local model for a specific task.

chat

Send a message to your local LLM and get a response.

# In Claude Code — just say it:
"Use the local model to write a SQL migration for adding a users table"
"Ask the local model to summarise this error log"
"Use local: write boilerplate for a new Go HTTP handler"

Parameters:

Parameter	Type	Default	Description
message	string	required	The prompt to send
system_prompt	string	""	Optional system prompt (overrides default)
temperature	float	0.7	Sampling temperature
max_tokens	int	512	Max response tokens
top_p	float	1.0	Nucleus sampling
top_k	int	0	Top-k sampling (0 = disabled)

Response format:

🏠 LOCAL · Qwen3-Coder-30B-A3B-Instruct-MLX-4bit

[model response here]

---
Tokens: 12 prompt + 48 completion = 60 total | 1.24s

---

quick_test

Run a predefined diagnostic prompt to benchmark your model and verify it's working.

quick_test hello       # intro prompt — tests basic response
quick_test code_review # Python snippet review — tests code understanding
quick_test math        # 347 × 28 — tests reasoning + speed

Response format:

Test: code_review
Prompt: Review this Python function: ...

Response:
[model code review]

---
🏠 LOCAL · Qwen3-Coder-30B-A3B-Instruct-MLX-4bit · 51.3 tok/s · 180 tokens · 3.51s

---

list_models

List the models available on your backend with descriptions.

list models

Response (oMLX with all four tiers loaded):

Models available at http://localhost:8000:

• DeepSeek-Coder-V2-Lite-Instruct-4bit-mlx
  ⚡ Turbo — ~135 tok/s, instant subagent calls, quick lookups & boilerplate

• Qwen2.5-Coder-7B-Instruct-4bit
  ⚡ Fast — ~80 tok/s, speed fallback, solid code quality

• Qwen2.5-Coder-14B-Instruct-4bit
  ⚖️  Everyday — ~28 tok/s, reliable default for most coding tasks

• Qwen3-Coder-30B-A3B-Instruct-MLX-4bit
  🧠 Quality — ~51 tok/s, best coding quality, MoE (3B active), no thinking mode

---

set_model

Switch the active model by name or fragment. The work-hours guard prevents accidentally loading big models during Grafana hours.

set_model(model_name="14b")           # fuzzy match → Qwen2.5-Coder-14B-Instruct-4bit
set_model(model_name="30b")           # fuzzy match → Qwen3-Coder-30B-A3B-Instruct-MLX-4bit
set_model(model_name="", force=True)  # clear override, auto-detect from backend

Parameter	Type	Default	Description
model_name	string	required	Model name or fragment (fuzzy matched)
force	bool	false	Bypass work-hours guard for big models

---

health_check

Verify your LLM backend is reachable and report what's loaded.

Response (oMLX):

{
  "status": "ok",
  "url": "http://localhost:8000",
  "models_loaded": "1/4"
}

Response (unreachable):

{
  "status": "unreachable",
  "url": "http://localhost:8000",
  "hint": "Make sure your LLM backend is running at http://localhost:8000."
}

---

get_config

Show current URL, active model, timeout, and work-hours guard state.

{
  "base_url": "http://localhost:8000",
  "active_model": "Qwen3-Coder-30B-A3B-Instruct-MLX-4bit",
  "model_source": "file",
  "timeout_seconds": 30,
  "work_hours_guard": false
}

---

set_work_hours_guard

Toggle a guard that blocks big model loads during weekday business hours (8am–5pm MT). Useful if you share system RAM with work VMs and don't want a 18 GB model load mid-meeting.

set_work_hours_guard(enabled=True)   # on — blocks big models 8am–5pm MT weekdays
set_work_hours_guard(enabled=False)  # off (default)

---

Offload-first (token thrift)

This server is built to absorb work that would otherwise spend Claude tokens.

Tier 1 — portable (zero config). When the server is connected, it advertises an offload-first instructions block, so any agent using it is told to route eligible work (summarize, boilerplate, single-file review, extract, explain, simple refactors) through the iterate tool first, tag a category, and keep multi-file reasoning + judgment on Claude.

The iterate tool. Runs a local-first escalation ladder: the active local model retries (feeding the gate's failure text back in) up to max_local_rounds, then optionally one attempt on a bigger local model (big_model), then escalates to Claude. Provide a gate so retries can improve:

• Structural: require_json, schema_keys, contains, regex, min_len.
• Executable: check_command — a shell command that reads the candidate at $CANDIDATE_FILE and exits 0 to pass (e.g. pytest, ruff).
• No gate → single local attempt, returned for you to verify.

Counts only are logged to ~/.omlx/mlx-call-log.jsonl (model, category, tokens, rounds, winning rung) — never prompt/response content.

Tier 2 — power-up (one command). Install Claude Code hooks + an /offload skill that reinforce the policy:

mlx-mcp-server install --claude-code --with-offload   # or --full for everything

---

Slash commands

Install with --full or --with-commands to get these in ~/.claude/commands/:

Command	What it does
/switch-model	List available models (queried live from oMLX, so new downloads appear automatically) and switch interactively
/mlx-help	Display a live reference card (pulls config via get_config)

---

Offload enforcement hook

A UserPromptSubmit hook classifies each prompt on the local model and, for offloadable work (summarize, extract, classify, draft, and single-file code), generates the answer locally and injects it as a draft for the assistant to verify — turning the offload policy from advisory into enforced. Logs counts/labels only (never prompt or response text) to ~/.omlx/mlx-call-log.jsonl and ~/.omlx/hook-decisions.jsonl.

Two failure modes

1. Silent quality gate escalation: If a local answer fails the quality gate (too short, code doesn't compile), it escalates silently to Claude without injecting a draft.
2. Loud infrastructure pause: If oMLX itself is unreachable (transport error, timeout, non-2xx), the hook runs omlx restart and injects a directive telling the assistant to surface the error and PAUSE — never a silent fallback to Claude.

Wiring it up (manual)

You must add this to ~/.claude/settings.json — the installer does NOT edit settings automatically:

{
  "hooks": {
    "UserPromptSubmit": [
      { "hooks": [ { "type": "command", "command": "mlx-offload-hook" } ] }
    ]
  }
}

mlx-offload-hook is installed on PATH via uv tool install mlx-mcp-server (~/.local/bin), and it reads oMLX credentials from ~/.claude/settings.json → mcpServers.mlx.env. After adding the hook, restart Claude Code.

---

Configuration

Set via environment variables, or use the install command to write them automatically.

Variable	Default	Description
MLX_BASE_URL	http://localhost:8080	Backend URL
MLX_DEFAULT_MODEL	""	Model name. If empty, auto-detected from /v1/models on first call
MLX_API_KEY	""	API key for secured backends (e.g. oMLX)
MLX_TIMEOUT	30	Request timeout in seconds

Auto-detection

When MLX_DEFAULT_MODEL is not set, the server queries /v1/models on the first chat call and uses whatever model the backend reports. The result is cached for the session. This works well for single-model backends (MLX LM, Ollama). For oMLX with multiple configured models, set MLX_DEFAULT_MODEL explicitly — oMLX lists all configured models, not just the loaded one.

---

Install command reference

mlx-mcp-server install [options]

Flag	Description
--claude-code	Target Claude Code (~/.claude/settings.json) instead of Claude Desktop
--base-url URL	Backend URL (default: http://localhost:8080)
--model NAME	Model name — optional, auto-detected if omitted
--api-key KEY	API key for secured backends
--with-commands	Copy slash commands to ~/.claude/commands/
--with-scripts	Copy helper shell scripts to ~/bin/
--full	Shorthand for --with-commands --with-scripts
--dry-run	Print the config that would be written without touching any files

Preview before writing:

mlx-mcp-server install --claude-code \
  --base-url http://localhost:8000 \
  --api-key mykey \
  --model "Qwen3-Coder-30B-A3B-Instruct-MLX-4bit" \
  --dry-run

Full install (MCP config + slash commands + scripts):

mlx-mcp-server install --claude-code \
  --base-url http://localhost:8000 \
  --api-key mykey \
  --model "Qwen3-Coder-30B-A3B-Instruct-MLX-4bit" \
  --full

---

Manual config

If you prefer to edit the config file directly:

Claude Desktop — ~/Library/Application Support/Claude/claude_desktop_config.json (macOS)

Claude Code — ~/.claude/settings.json

{
  "mcpServers": {
    "mlx": {
      "command": "mlx-mcp-server",
      "env": {
        "MLX_BASE_URL": "http://localhost:8000",
        "MLX_DEFAULT_MODEL": "Qwen3-Coder-30B-A3B-Instruct-MLX-4bit",
        "MLX_API_KEY": "your-key-here"
      }
    }
  }
}

---

Supported backends

Backend	Platform	Default port	Notes
oMLX	macOS (Apple Silicon)	8000	Requires API key + explicit model name
MLX LM	macOS (Apple Silicon)	8080	No auth needed, model auto-detected
Ollama	macOS / Linux / Windows	11434	Set MLX_DEFAULT_MODEL to model name
LM Studio	macOS / Windows	1234	Enable "Local Server" in LM Studio

---

oMLX-specific notes

oMLX is a native macOS GUI for running MLX models on Apple Silicon. A few quirks to know:

• Port: listens on 127.0.0.1:8000 (not 8080)
• API key required: set one in oMLX settings and pass it via --api-key
• Model field required: oMLX returns 422 if model is omitted from requests — always set MLX_DEFAULT_MODEL
• /health endpoint: unauthenticated, returns engine pool info — health_check uses this first
• MoE models: Qwen3-Coder-30B-A3B-Instruct-MLX-4bit activates only ~3B params per token — faster than dense 14B models at higher quality
• Thinking models: Disable the "Enable Thinking" toggle in oMLX Advanced settings for any Qwen3 general or Qwen3.6 model before using it as a subagent. Thinking mode burns thousands of tokens before each answer.
• enable_thinking payload: The client only sends this field when explicitly True. Sending enable_thinking: false unconditionally causes 400 errors on models that don't recognise it.
• DFlash / speculative decoding: Disable DFlash for Gemma models in oMLX — it routes output to reasoning_content instead of content, causing empty responses.

---

Requirements

• Python 3.11+
• A running OpenAI-compatible LLM backend

---

Development

git clone https://github.com/deresolution20/mlx-mcp-server
cd mlx-mcp-server

# Install with dev dependencies
uv sync --dev

# Run tests
uv run pytest tests/ -v

# Install locally for testing
uv tool uninstall mlx-mcp-server 2>/dev/null
uv tool install . --no-cache

---

License

MIT