FitLLM MCP server

FitLLM Engine

FitLLM is an open-source, zero-dependency engine that checks whether a local LLM fits on a GPU or Apple Silicon Mac using architecture-aware memory math.

Live: https://fitllm.run · Bilingual · Free · No ads · No login

Open engine: fitllm-engine (MIT · npm fitllm-engine · npx fitllm)

Zero dependencies. One readable file: engine.js. Conformance-vector tested. MIT.

Install

# self-contained binary — no Node required
curl -fsSL https://fitllm.run/install.sh | sh

# Homebrew (tap)
brew tap click6067-ship-it/fitllm https://github.com/click6067-ship-it/fitllm-engine
brew install fitllm

# Windows (Scoop)
scoop install https://raw.githubusercontent.com/click6067-ship-it/fitllm-engine/master/packaging/fitllm.json

# already have Node? nothing to install
npx fitllm "Gemma 4 12b" --gpu "RTX 4090"

Binaries for macOS (arm64/x64), Linux (x64/arm64, glibc and musl) and Windows x64 are attached to every release with a .sha256 next to each one; install.sh verifies the checksum and installs nothing if it does not match.

Two things stated plainly rather than buried: each binary embeds its JavaScript runtime, so it is 60–94 MB — much larger than an equivalent Rust or Go tool, which is the price of not forking the engine into a second language. And this is a Homebrew tap, not homebrew-core: core's bar for a self-submitted project is 225 stars / 90 forks / 90 watchers, which this project does not meet yet.

Quick start

npx fitllm "Gemma 4 12b" --gpu "RTX 4090"     # one line, exit 0 fits / 1 won't — run before you download
npx fitllm --top --gpu 4090                    # what can this hardware run?
npx fitllm --top --detect --json               # detect every supported local GPU; agent-ready JSON
npx fitllm Qwen/Qwen3-32B --detect --json      # public Hugging Face ID or URL; unsupported configs fail closed
npx fitllm "Gemma 4 12b" --detect --json --why # include architecture, evidence, assumptions, and exact memory inputs
npm install fitllm-engine                      # use the same engine as a library (see Usage)

Remote MCP server

Connect any Streamable HTTP MCP client to https://fitllm.run/api/mcp:

{
  "mcpServers": {
    "fitllm": {
      "url": "https://fitllm.run/api/mcp"
    }
  }
}

Tools

• checkllmfit — check one model against a GPU, multi-GPU rig, or Mac and return the verdict, memory breakdown, and a fix when it does not fit.
• whatfitson_hardware — rank the supported local models that fit the given GPU, multi-GPU rig, or Mac.
• list_supported — list the built-in model and hardware names accepted by the fit checker.

The server is read-only, stateless, and requires no authentication.

npx fitllm "GLM-4.7-Flash" --gpu 4090     # ✓ FITS — 21.9/24 GB, free 2.1 GB
npx fitllm "gpt-oss-120b" --mac 64        # ✗ WON'T FIT → what to change to make it fit
npx fitllm "Qwen 3.6 35B" --gpu "5090 + 3090"   # multi-GPU rig — VRAM pools (56GB), even mixed cards
npx fitllm --top --detect --json          # detect hardware + what fits, for people or agents
npx fitllm "Gemma 4 12b" --detect         # one verdict on this machine

Shortened. The full README is on GitHub.