ai-detect - an open source AI detector that runs on your own machine

Is the copy you're buying handwritten? Find out, free and at scale.

ai-detect is a free, open source AI text detector that runs entirely on your own hardware. It scores writing sentence by sentence using desklib/ai-text-detector-v1.01, a 304-million-parameter DeBERTa-v3-large model that ranked first on the RAID detection benchmark. There is no API key, no per-word pricing and no upload: after a one-off 1.7 GB model download it works offline, on CPU or GPU. It ships as a command-line tool, a Python package and an MCP server, under the MIT licence.

That combination is the point. Every mainstream AI checker - GPTZero, Originality.ai, Copyleaks, Winston - is a hosted service you paste your client's unpublished draft into. This one never sends a byte anywhere.

It isn't Pangram Labs, and no detector is a lie detector - a confident writer who contracts their verbs will sail through. But where there's smoke there's fire, and across a batch of copy the signal is real.

Quick answers

Question	Answer
Does it cost anything?	No. MIT licensed, no API key, no usage limits.
Does my text leave the machine?	No. Inference is local; the only network call is the first model download.
Which model?	DeBERTa-v3-large (304M), RAID benchmark #1. A 126 MB RoBERTa ONNX alternative ships too.
Can I self-host it as an API?	It runs as an MCP server (ai-detect-mcp) and as an importable Python package.
Does it need a GPU?	No. CPU by default; CUDA used automatically when present.
How accurate is it?	On paired tests, formal phrasing scored 92.6% AI against 0.03% for the same fact written conversationally. Treat it as a signal across a batch, not a verdict on one sentence.

What it tells you

Better than a single percentage, it tells you why a line reads as machine-written. The patterns are mapped from 70+ paired sentence tests, formal version against a conversational rewrite of the same information:

• Missing contractions are the #1 signal. "The software has been significantly improved" scores 92.6% AI; "software's got a lot better" scores 0.03%.
• "Provides / offers / delivers" are detector magnets. So are the "Furthermore" / "Additionally" / "In conclusion" openers.
• "For [group] who [condition]" framing, vague abstractions where a specific name would do, and, oddly, the word "noticeably".

Each flag comes with a plain-English rewrite suggestion, so the tool doubles as an editing pass. The full pattern write-up is in docs/detection-patterns.md.

  Model AI score: 87.1% - LIKELY AI   [desklib]
  Sentences: 3 AI / 0 Human / 3 scored
  SDSL: mean=7.3 words, stddev=1.9, CV=0.26 (very uniform (AI-like))
  Patterns: 1 flaggy adverb, 1 formal verb, 1 formal transition

  >> AI  (0.92) The software has been significantly improved.
              ^ flaggy_adverb: 'significantly' — try 'a lot' or 'massively' or cut it
  >> AI  (0.73) Additionally, the QR2 provides excellent stability.
              ^ formal_verb: 'provides' — try 'gives you' or 'has'
              ^ formal_transition: 'Additionally' — cut it, or use 'And' / 'Plus'

Two detectors

	desklib (default)	light (--model light)
Model	DeBERTa-v3-large, 304M	RoBERTa-base int8, ONNX
Download	~1.7 GB, once	~126 MB, once
Runtime	PyTorch (CPU or CUDA)	ONNX Runtime (CPU, or GPU via DirectML/CUDA)
Best for	the calibrated reference score	a fast, small triage pass

desklib is the one the pattern research was built on and the one I trust for an absolute score. light is smaller and quicker to install and it runs hotter — it over-flags a bit — so treat it as a fast first look rather than the final word. Same CLI, same MCP tools, just pass --model light.

Why a local detector rather than a hosted one

The hosted AI checkers - GPTZero, Originality.ai, Copyleaks, Winston AI - all work the same way: you paste the text into their site, their server scores it, you pay per word or per month. For a lot of jobs that's fine. For three, it isn't.

Client confidentiality. If you're vetting commissioned copy, that draft is unpublished and often under NDA. Pasting it into a third-party scoring service is a disclosure, whatever the privacy policy says. Running the model locally makes the question moot.

Volume. Checking sixty articles from an agency costs nothing here beyond electricity. Per-word pricing turns the same batch into a purchase order.

Reproducibility. A hosted model can be retrained on a Tuesday and score your archive differently on Wednesday, with no changelog. A pinned local checkpoint gives you the same number in six months, which matters if the score is going in a report.

The trade is real: you give up a polished dashboard, team accounts and a support contract, and you spend 1.7 GB of disk. As of August 2026 this is beta software and the honest positioning is a signal across a batch, not a verdict you'd take to arbitration.

Install

git clone https://github.com/houtini-ai/ai-detect
cd ai-detect
pip install .            # CLI + MCP server (pulls torch, transformers, mcp)
pip install ".[light]"   # add the small ONNX model (onnxruntime)

That gives you two commands on your PATH: ai-detect (the CLI) and ai-detect-mcp (the MCP server). Prefer not to install? pip install torch transformers and run python detect.py ... from the repo — the old entry point still works.

Looking for detect.py?

If you came from the article and opened detect.py expecting the whole program, you'll have found fourteen lines and assumed something was missing. Nothing is — the file is a shim that keeps python detect.py ... working, and the implementation moved into the ai_detect/ package when this grew past one file:

File	What's in it
ai_detect/detector.py	Model loading and scoring - both backends live here
ai_detect/patterns.py	The pattern diagnostics (formal verbs, missing contractions, SDSL)
ai_detect/cli.py	The command-line interface
ai_detect/server.py	The MCP server
detect.py	Backwards-compatible shim - imports and calls ai_detect.cli

Everything is in the repo and nothing is behind a paywall or a gist. Start at ai_detect/detector.py if you want to read how the scoring works.

Check your setup any time:

python scripts/check_env.py

Run it

A CUDA GPU helps but isn't required — it defaults to CPU and uses the GPU automatically if one's there.

ai-detect --file draft.txt              # score a file
ai-detect --text "your text here"       # score a string
ai-detect --compare a.txt b.txt         # compare two versions
ai-detect --json --file draft.txt       # machine-readable output
ai-detect --model light --file draft.txt   # small/fast model
ai-detect --device cpu --file draft.txt    # force CPU (auto | cpu | cuda)

Try it on the bundled examples — one obviously machine-written, one not:

ai-detect --compare examples/ai-sample.txt examples/human-sample.txt

Only the copy-heavy sentences get scored: anything under five words (headings, fragments) is skipped rather than guessed at.

Use it as an MCP server

ai-detect is also a Model Context Protocol server, so Claude (Desktop, Code, or any MCP client) can run detection for you — including on files, where the server reads the draft so it never has to be pasted into the chat.

Add it to your MCP client config:

{
  "mcpServers": {
    "ai-detect": {
      "command": "ai-detect-mcp"
    }
  }
}

If ai-detect-mcp isn't on your PATH, use the full Python invocation instead:

{
  "mcpServers": {
    "ai-detect": {
      "command": "python",
      "args": ["-m", "ai_detect.server"],
      "cwd": "C:\\path\\to\\ai-detect"
    }
  }
}

Tools it exposes:

Tool	What it does
detect_ai_text	Score a string of text, sentence by sentence
detect_ai_file	Score a local file (server reads it — keeps big drafts out of context)
compare_texts	Score two texts and report the delta
get_model_status	Report instantly whether a model is ready, still downloading, or absent
list_models	List the available models, their sizes, and download state

The model & the download

First run of the default model pulls ~1.7 GB from the Hugging Face Hub and caches it under ~/.cache/huggingface. After that it's instant and offline. Nothing about your text is sent anywhere — the model runs on your hardware.

First run through MCP: the first detect call waits for the download. The server starts fetching the weights in the background the moment it launches, so the connection itself is never held up — but a detect call issued before that finishes has to wait for it, which can be a few minutes. get_model_status returns instantly and distinguishes ready / downloading / absent, so the client can check before detecting and tell you what's actually happening rather than looking like it has hung. Claude will typically do this for you; you can also just warm the cache once from the CLI:

ai-detect --text "warming the cache"

Every call after that, CLI or MCP, is instant. --model light (~126 MB) downloads fast enough that it rarely trips this. (The MCP server also spends a few seconds importing its ML libraries at startup — that's expected, and it happens in the background.)

If a download stalls outright, a detect call gives up after 15 minutes with an explanatory error instead of hanging forever. Set AI_DETECT_READY_TIMEOUT (seconds, 0 = wait indefinitely) to change that.

Why local and not a hosted API? desklib registers a custom model architecture, so it isn't served by Hugging Face's hosted inference — and even where a hosted detector exists, using it would mean shipping your unpublished copy to someone else's server. For a tool you point at commissioned work, local is the right default. If 1.7 GB is too much, --model light is a ~126 MB stand-in.

Status

Beta, and honest about it. It's a CLI I run on my own commissioned copy: the model does the classification, the pattern diagnostics and rewrite hints are mine. Expect rough edges. If it's useful to you, that's a bonus.

Built by Houtini.