aidetect 0.1.0

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🔍 What is this

A command-line tool that reads a .docx or .txt and scores each paragraph 0–1 on how AI-generated it reads, using the desklib/ai-text-detector-v1.01 DeBERTa model — the one sitting at #1 on the RAID benchmark. Everything runs on your own machine; after the first model download it never touches the network. You point it at your Extended Essay, it tells you which paragraphs sound like a language model wrote them.

The point isn't to cheat a detector. It's the opposite: I write my own drafts, and sometimes my own honest prose still trips these classifiers because that's what earnest formal writing looks like to them. This flags those paragraphs so I can reword before a teacher runs Turnitin and has an awkward conversation with me about it.

It is directional, not oracular. A high score means "reword this," not "you're caught." It is not, and cannot be, the number Turnitin shows a teacher.

nick@aidetect:~$ aidetect score EE-clean.txt
P  1   0.08  [##------------------]
P  2   0.71  [##############------]  <-- AI-ish
average AI score: 0.34   |   1/6 paragraphs flagged
reminder: directional only, not a Turnitin score.

🧠 The detection engine

🚀 Run it

uv tool install aidetect      # or: pipx install aidetect

aidetect                                   # list the five subcommands
aidetect count "draft.docx" --limit 4000   # IB word count, by section
aidetect count "draft.docx" --json         # same, as one JSON object
aidetect score "draft.docx"                # score a whole draft
aidetect score --text "one sentence"       # score a single string
aidetect bino  "draft.docx" --mlx --pair gemma

count and extract are instant and need no model. score and bino need a machine that can hold a transformer: built and tested on an 18GB Apple Silicon Mac, MPS-accelerated. Their first run downloads the model and will sit there for a minute — that's normal, not a hang. Every run after is fast and offline.

On Apple Silicon the Gemma 4 MLX pair installs automatically. Elsewhere it is skipped and the Qwen pairs still work.

--json

count takes --json and prints exactly one object on stdout, nothing else:

{"sections": [{"title": "Introduction", "words": 812}], "total": 3940, "limit": 4000, "over": -60}

Every key is always present. limit and over are null when no --limit was given — that means "does not apply", not "could not be read". A draft with no prose is an empty sections list and exit 0. Errors go to stderr with a non-zero exit, so consumers branch on the exit code rather than parsing error text.

🔩 Under the hood

flowchart LR
    A[.docx / .txt] --> B[aidetect extract<br/>strip non-prose]
    B --> C[read_paragraphs<br/>>= 25 words]
    C --> D[desklib DeBERTa<br/>mean-pool + sigmoid]
    D --> E[per-paragraph<br/>0-1 score + flags]

🔭 Binoculars: shelved, then revived by Gemma 4

Binoculars is a training-free detector: run text through two LMs that share a tokenizer (a base "observer" and an instruct "performer") and divide perplexity by cross-perplexity. Its designed model pair is Falcon-7B ×2 (~28GB) — too big for an 18GB Mac, so the fallback was a small same-family pair (Qwen2.5-0.5B or 1.5B) that fits.

aidetect calibrate scores a labelled set — mine is 12 real pre-2020 IB Extended Essay paragraphs vs 12 LLM-written ones on the same topics — and finds the best separating threshold. Measured across pairs:

The Qwen pairs sit near a coin flip: their human and AI score clusters almost completely overlap, because the perplexity gap Binoculars exploits is sharp in larger models and mush in sub-2B ones. That was the original negative result. Swapping in a Gemma 4 pair opens a clean gap (human mean 0.90 vs AI 0.71) and separates the set at 96%. Gemma 4 ships as a multimodal checkpoint, so --mlx quantizes it to 4-bit and runs it text-only through mlx-vlm, fitting the 18GB Mac in ~6GB:

aidetect bino IA-clean.txt --mlx --pair gemma   # uses the shipped threshold

# refit the threshold on your own labelled set
aidetect calibrate --human-dir corpora/human --ai-dir corpora/ai --mlx --pair gemma

desklib stays the primary detector; Binoculars is now a usable second opinion rather than a dead end. The calibration sets are not shipped with the package — clone the repo to reproduce the numbers, or point --human-dir/--ai-dir at your own. Your fitted threshold lands in ~/.config/aidetect and takes precedence over the shipped one, so it survives an upgrade.

🧪 The peer set: genre context, not a human class

The 12 human samples are Extended Essays: English, History, Biology, Physics, Philosophy. A CS IA is a different animal, all database schemas, GUI components and method-by-method justification, and technical prose is inherently more predictable token-by-token, which drags perplexity-ratio scores down no matter who typed it. So a CS IA scoring below the EE human mean means less than it looks.

corpora/peer/ holds 12 paragraphs of real IB Computer Science IA prose (5 projects, 5 authors: sudokuMaster, IBOrganizer, MyCalendar, and two IBO-published new-syllabus specimens). Measured against the same anchors:

The genre gap is real and it is about 0.05 on Binoculars. Score your IA against peer, not against human.

It is not a human class and it never fits a threshold. Every source postdates ChatGPT; three of the five were written in 2025. None carries an authorship attestation, and in 2025 a fair share of student IAs were not written unaided. Fold that into human/ and any AI-assisted sample drags the mean down, lowers the threshold, and the tool starts clearing drafts for the wrong reason, a detector that reassures instead of measures. aidetect calibrate reads only the two folders you name, so peer/ stays out of threshold fitting by construction, not by discipline.

What it can tell you: "my prose scores like other IAs in this genre." What it can never tell you: "my prose is human." Matching a set you cannot vouch for proves you are not an outlier, nothing more.

Stack: python · pytorch · transformers · mlx-vlm · desklib DeBERTa

The lighter cross-check tool lives at Ejhfast/fast-ai-detector — it's a separate repo, not vendored here.