✍︎ Signs of AI Writing

Are you a teacher? Start here → — what this does and what it cannot do, in plain language, with the error rate drawn rather than tabulated. No badges, no interval notation, nothing to install. English & Spanish.

Try the live demo → — English & Spanish, runs in your browser. No signup, and the analysis uploads nothing.

Use it in your editor → — an agent skill for Claude Code, Codex, Gemini CLI and Cursor, in one line: npx skills add peopleworks/SignsofAI -g. It edits by the same rules this engine scores by, and it never invents a number.

Download the Windows app → — the same tool in a window. An installer that needs no administrator rights, with the .NET runtime bundled; a .zip too, if you would rather not.

Real recording of the live demo — the score updates as you type, and every highlight comes with a suggested fix.

Rather watch than read? The two-minute explainer: English · Español

A free, privacy-first toolkit for academic and writing integrity. It does two things:

1. De-AI-ify linter — flags the tells of AI-generated writing (overused vocabulary, rhetorical crutches, robotic sentence rhythm) and, for every finding, tells you how to fix it.

2. Originality checker — "did they write it, or copy it?" Compares documents against each other and surfaces the passages they share — verbatim copies, reworded paraphrases (even across languages), and a whole-cohort overview — as evidence a human judges. Not a black-box verdict.

🔒 The analysis runs entirely in your browser, and nothing is uploaded to run it. No account, no telemetry, no server that sees your text.

Four features can send text off the device, and not one of them runs unless you turn it on, each disclosed in the interface at the moment you choose it: the paraphrase check and the perplexity measurement (both call a server you or we host), the live rewrite when you supply your own API key — the key stays on your device, the text goes to the provider you picked — and the optional web spot-check for a distinctive phrase, which exists only if the operator configured a search provider.

Everything else — every rule, the score, the character scan, the citation cross-check, the writer baseline, the report — is computed locally and stays there. In the desktop app, the perplexity measurement is local too.

The Windows app can also check whether a newer version has been published, because it has no auto-update and never will. That is not one of the four: it sends no text, no account and no identifier — one request to GitHub's public release list, the same one a browser would make. It asks before its first check, at most one a day, and it never downloads or runs anything for you.

Built with .NET 10 and Blazor WebAssembly by Pedro Hernández (PeopleWorks), Microsoft MVP for .NET — for the .NET and Microsoft developer community, por y para la comunidad educativa.

Repo: https://github.com/peopleworks/SignsofAI

English and Spanish are supported in two independent ways:

• The interface switches EN ⇄ ES instantly from the toolbar — no page reload, remembered per browser, and it follows your browser's language on a first visit. Translations are plain JSON files anyone can contribute: see Translating the interface.

• The analysis runs against a per-language rule-pack, auto-detected or selectable. The Spanish rule-pack is an original derivation of AI-writing markers for Spanish.

The two are separate on purpose, so findings stay in the language of the text being analyzed: advice about English prose is given in English even when the interface is in Spanish, because that's the language the advice is about.

How often is it wrong about a human?

Every AI detector gets asked this and almost none of them answer. Docs/CALIBRATION.md is the answer, measured against 296 texts written before 2022 — open-access research articles, pre-2022 encyclopedia revisions in both languages, and 206 classroom essays by adult learners of English, one per student, from a corpus collected between 2006 and 2012.

At a threshold of 30/100 it flags 2 of them: an observed 0.7%, with a 95% interval reaching 2.4%. The recommendation is made from the uncertain end of the interval rather than the flattering one, so it stays cautious while the corpus is small, and it follows the data in whichever direction they move as the corpus grows.

The learners are the group this whole category is accused of harming — studies report that other detectors flag 61% of their essays — and they are the reason the boundary sits at 30 rather than the 25 it sat at before they joined: at 25 the tool flagged 9 of their 206 essays, 4.4%, and none of the 90 published texts. That figure is on the page, by group, rather than averaged away. It is far below the numbers reported for other tools, and it is not zero.

It is deliberately not an accuracy figure. Accuracy needs a collection of machine-written text, which is a sample of whichever models were around that month; a false-positive rate needs only human writing, and it measures the harm this category actually causes — studies report that detectors flag 61% of essays by non-native English speakers, and none of them publish that about themselves.

The report also names which rules misfire, ranked. That list is uncomfortable and it is the most useful thing the exercise produces.

The corpus is a JSON manifest anyone can extend, the tool that builds and measures it is in tools/SignsOfAI.Calibration, and the whole thing re-runs in one command. See Docs/Calibration/README.md — Spanish academic writing is the most wanted contribution.

Related MCP server: Byakugan: Private, open-source AI-text checker

For teachers: the part that is not software

A detector is not what you need first. Docs/Teaching/ is syllabus language you can paste, a one-page sheet to hand students before anything goes wrong, and a procedure for the day a question becomes formal — all bilingual, all free of any licence, attribution or permission.

None of it requires this tool. It exists because the hard part of AI writing in a classroom was never detection; it is what you do on the morning you suspect something and have nobody to ask. All three documents are built on the same rule: a score is never the reason for a decision about a student, and a conversation about the work settles what no software can.

1. The AI-writing linter ("Analyze")

Unlike black-box detectors that only spit out a score, this is an explainable, actionable, educational linter. Paste, upload (.docx / .txt / .md), or just start typing — the 0–100 score, highlights, statistics, and per-finding fixes update as you write.

• Sentence-rhythm visualization — a per-sentence bar chart that makes burstiness visible.

• Per-finding recommendations — every flagged tell carries a concrete fix and the research behind it.

• Live rewrite (on-device, no key) — your text and a de-AI-ified version side by side, rebuilt on every keystroke, with the score dropping as you go. It runs off the rule-pack — no model, no network, no API key — so it is instant and free. Every change is listed with alternatives to pick from and a one-click leave this one alone. Three strengths, from only the strongest tells to delete the empty intensifiers too.

  It only does what a word swap can honestly do, and declines the edits it would get wrong: it won't turn "delve into" into "examine into", won't drop the "just" that a "not just X, it's Y" construction depends on, and won't put "el" in front of a feminine noun. Rhythm and rhetorical structure need real rewriting, so those stay in the recommendations — and the panel says how many.

• Humanize (optional, BYOK) — connect an AI provider and rewrite the flagged text in one click. Anthropic (claude-opus-4-8, works from the browser), OpenAI / DeepSeek, Azure OpenAI, or Ollama (local, no key). Credentials live only in your browser and are sent directly to the provider.

• Before/after diff and a shareable result card (a PNG summary that never includes your text).

• Custom catalogs (BYO rules) — paste banned words or import a rule-pack JSON; merges live.

• Catalog page — a searchable library of every AI-writing sign, in both languages, ranked with an in-browser BM25 index.

This is the difference: not "87% AI", but which words, why they were flagged, and what to write instead.

2. The Originality checker ("Originality")

"¿Lo escribió la IA, lo copiaste, o lo parafraseaste para esconderlo?" Drop in two or more documents — a thesis and its sources, a batch of student submissions — and see exactly what they share. The guiding principle is honest: we surface the evidence and highlight it; a human judges. We never accuse. This is not a whole-internet index like Turnitin.

• Shared-passage evidence — matches are highlighted in both documents, side by side; the headline overlap number equals exactly what you see highlighted (the evidence is the score).

• Phase B is the one feature that leaves the device. It's opt-in, disclosed in the UI, and sends only the sentences you choose to check to the PeopleWorks server. Everything else stays on your machine.

• Phase D is deliberately honest: we can't index the whole web, so instead of pretending to, we surface the passages worth checking and prepare the searches — nothing is sent anywhere until you click one. An optional automatic web search can be enabled by the server operator (see Optional server below).

A whole class at a glance: every document against every other, then the shared passages themselves — evidence, not an accusation.

3. The predictability meter (optional server)

An honest reframing of perplexity. A small language model (Qwen2.5-0.5B or Microsoft Phi-4-mini, int8 ONNX) measures how predictable / generic a text's phrasing is. This is not an AI-vs-human verdict — on a labelled corpus the two overlap badly (memorized human text scores predictable too). We surface predictability honestly as one signal among many, calibrated per language. Opt-in; runs on the PeopleWorks server. The model lazily loads and idle-unloads to keep the server light.

4. Use it from other apps — MCP server

Everything above is also available to Claude Desktop and any MCP client through SignsOfAI.Mcp, a Model Context Protocol server (built on the official ModelContextProtocol SDK, stdio transport). Because the engine lives in SignsOfAI.Core — pure .NET, no browser — the server just exposes it as tools:

The first eight run entirely on the machine; the last two disclose that they send text to the server (endpoint via the SIGNSOFAI_API_ENDPOINT environment variable).

It ships on NuGet as SignsOfAI.Mcp, so nothing needs building. Point Claude Desktop at it:

// %APPDATA%\Claude\claude_desktop_config.json
{ "mcpServers": { "signs-of-ai": {
  "command": "dnx",
  "args": ["SignsOfAI.Mcp", "--yes"]
}}}

Or install it as a global tool once — dotnet tool install --global SignsOfAI.Mcp — and use "command": "signsofai-mcp". See src/SignsOfAI.Mcp/README.md for details.

VS Code: the package ships an MCP manifest, so its NuGet page has an MCP Server tab with the config already generated — copy it into .vscode/mcp.json and you're done.

5. Use it as an agent skill — /signs-of-ai

The skill has its own page →, with the two modes side by side and what it refuses to do.

Prefer to work inside your editor? SKILL.md is a drop-in agent skill that de-slops a draft — or reports the tells a text carries — in English and Spanish. It is a human-readable distillation of the same rules.en.json / rules.es.json taxonomy, so it edits by the same rules the engine scores by.

# Claude Code, Codex, Gemini CLI, Cursor and the rest, in one command
npx skills add peopleworks/SignsofAI -g

# …or as a Claude Code plugin, from the marketplace manifest in this repository
/plugin marketplace add peopleworks/SignsofAI
/plugin install signs-of-ai

Then:

/signs-of-ai            <your draft>          # edit mode: rewrite + change summary
/signs-of-ai is this AI slop?  <the text>     # examine mode: the tells, quoted, no rewrite

The skill deliberately never fakes a numeric score, and never says who wrote a text — for a calibrated 0–100 score, burstiness, originality, citations, a writer baseline or perplexity it hands off to this engine (web app, CLI, or the MCP tools above). It carries the same six rules about what a finding may claim that the report does, including the error rate that has to travel with any score. See skill/README.md.

6. Use it where the writing happens — the Word add-in

A task pane inside Word. Press Read the signs on the Home tab and it reads the open document and answers in the sidebar: no copying into a browser, no uploading a file, no leaving the page you are writing on.

It is the same engine, not a smaller one. Every rule, the character scan, the citation cross-check and the verdict rules arrive through SignsOfAI.UI, the class library the web app and the desktop app also render. Word is simply a third host.

Why a task pane is the right place for this particular tool

A task pane is a browser. The WebAssembly engine is downloaded once and runs there, on the machine, which means the document is never uploaded. It is the guarantee the web app already makes, in the application where the document actually lives.

That is not a nicety. Every other add-in in this category posts your text to an API, because their analysis is a server. Ours is not, so there is nothing to post it to. And the manifest asks for ReadDocument, not ReadWriteDocument: Word itself enforces that this add-in can only read your document, rather than asking you to trust a sentence on a website.

What it looks like on a real document

That is Word on the web (the address bar is in the picture) with a 357-word document open, and the pane is worth reading twice.

It refused to give a verdict, and printed why: the corpus this build is calibrated on contains no text shorter than 649 words, so below that there is nothing to compare against and the score is "neither evidence that a machine wrote this nor evidence that a person did." See the calibration.

And it still found six no-break spaces, because the character scan is a fact about the file rather than a judgement of its prose. It carries no threshold, so it holds at any length, and it says nothing about who wrote anything, which the panel states in as many words.

A tool that answers everything is easy to build. This is the other kind.

Installing it

The add-in's page → — what it does, both install routes, and what it refuses to do, in English and Spanish.

The short version: on the web it is Home → Add-ins → More Add-ins → My Add-ins → Upload My Add-in with src/SignsOfAI.Word/manifest.xml. Word for Windows has no upload button and reads a shared-folder catalogue instead, which src/SignsOfAI.Word/README.md walks through.

PowerPoint is a different product, on purpose

A deck rarely reaches 649 words, so the same add-in in PowerPoint would mostly do what it did above: withhold the verdict. Correct, and not much use. What does work at slide length is the part with no threshold — the character scan and the named tells — so the honest question there is "does this deck carry a humanizer's fingerprints", not "is this AI". That is a different product and it is not built yet.

Architecture

SignsOfAI.slnx
├─ src/
│  ├─ SignsOfAI.Core            # Pure C# engines (no UI/server deps)
│  │  ├─ Analyzers/             # Lexical, Pattern, Burstiness (IAnalyzer)
│  │  ├─ Originality/           # OriginalityChecker (shingles+tiling), ParaphraseFinder,
│  │  │                         #   DistinctivePhraseExtractor
│  │  ├─ Rewriting/             # LocalRewriter — on-device de-AI-ifying, no model or network
│  │  ├─ Rules/Packs/           # rules.en.json, rules.es.json (embedded, community-extensible)
│  │  ├─ Text/                  # Tokenizer, sentence splitter, language detector, statistics
│  │  └─ AiWritingAnalyzer      # Public facade: Analyze(text, language)
│  ├─ SignsOfAI.UI              # The whole interface (Analyze, Originality, Catalog) — shared by
│  │  │                         #   both hosts below, so a change lands in web and desktop at once
│  │  └─ wwwroot/i18n/          # UI translations: en.json, es.json + locales.json (community-extensible)
│  ├─ SignsOfAI.Web             # Host: Blazor WebAssembly, runs in the browser
│  ├─ SignsOfAI.Desktop         # Host: WPF + WebView2, runs offline and reaches local models
│  ├─ SignsOfAI.Cli             # `dotnet tool` for CI pipelines
│  ├─ SignsOfAI.Mcp             # MCP server (stdio): the engine as tools for Claude Desktop / any client
│  └─ SignsOfAI.Perplexity.Api  # Optional ASP.NET Core server: predictability + embeddings
│     ├─ Engine/                #   OnnxPerplexityEngine, OnnxEmbeddingEngine (lazy-load + idle-unload)
│     └─ Config/                #   model profiles, calibration, embedding + web-search options
└─ tests/
   └─ SignsOfAI.Core.Tests      # xUnit (120+, incl. guards for the community locale files)

The Core engines are decoupled from the UI and server — the CLI, the Blazor app, and the API all reuse them.

Run it

dotnet run --project src/SignsOfAI.Web
# then open http://localhost:5019

Test

dotnet test

Command line & CI (dotnet tool)

The linter ships as a global tool so you can gate prose in CI:

dotnet tool install --global SignsOfAI.Cli

signsofai check README.md                 # pretty report
signsofai check article.docx --lang en    # Word documents too
signsofai check post.md --json            # machine-readable
signsofai check post.md --max-score 40    # exit 1 if it reads too much like AI → fails CI
signsofai check post.md --rules my-style.json   # your custom catalog
signsofai check ensayo.txt --lang es --reader-lang en --report out.md

--lang is the language of the text; --reader-lang is the language of whoever reads the output — the evidence report, the character scan and the citation cross-check, all of which address that person rather than describe the prose. It defaults to the text's language, so you only pass it when the two differ. Findings stay in the text's language on purpose: a Spanish tell is explained in Spanish.

The analysis engine is also a library — dotnet add package SignsOfAI.Core:

var result = new SignsOfAI.Core.AiWritingAnalyzer().Analyze(text, "auto");
Console.WriteLine($"{result.OverallScore}/100 — {result.Verdict}");

Optional server (SignsOfAI.Perplexity.Api)

The client works fully on its own; this server only powers the opt-in features (the predictability meter and the Phase B paraphrase check). It's ASP.NET Core (.NET 10) hosting ONNX models with lazy-load and idle-unload so it stays light. Model files are not in git — they download on first use.

The client points at a hosted instance by default; to run your own, set the endpoint in the app's server settings and configure CORS for your origin.

Enabling the optional automatic web search (Phase D)

By default Phase D is the on-device, one-click-search experience (no key, nothing sent until you click). An operator can additionally enable an automatic web search — useful for presentations — by configuring a search provider on the server (the key never touches the browser). It stays off unless configured:

// appsettings.json (or environment variables)
"WebSearch": {
  "Enabled": true,
  "Provider": "brave",              // Brave Search API (free tier); provider-abstracted
  "ApiKey": "",                     // prefer the BRAVE_API_KEY environment variable
  "MaxPhrasesPerDoc": 8,
  "MaxResultsPerPhrase": 5
}

When enabled, the server advertises the capability and the client offers an automatic "search the web" action that reports pages containing a passage verbatim. If it's off, quota-exhausted, or errors, the UI falls back to the manual one-click searches — it never breaks.

Extending the rules

Add entries to src/SignsOfAI.Core/Rules/Packs/rules.<lang>.json — lexical rules match single word tokens, pattern rules are regexes for multi-word tells. Each sets a weight, severity, and suggestion.

A lexical rule can also tell the live rewriter what to do, which suggestion cannot: that field is prose for a person ("mix, blend, range — or just name the thing"), and a program shouldn't be reading intent out of prose.

{ "id": "lex.utilize",  "terms": ["utilize", "utilizes"], "weight": 3.5, "severity": "Medium",
  "suggestion": "use",  "replacements": ["use"] },              // what to substitute, best first
{ "id": "lex.just",     "terms": ["just"],                "weight": 1.0, "severity": "Info",
  "suggestion": "empty intensifier — usually deletable", "delete": true }   // remove the word instead

Both are optional. Without them the rewriter falls back to reading a comma-separated list off suggestion, and refuses to guess at anything else — a lone term could be a replacement ("use") or a description ("muletilla"), and telling them apart needs to know the language. So a rule with no explicit field is simply reported and never auto-edited, which is why every built-in rule states its fix outright (there's a test that keeps it that way).

Translating the interface

If you speak a language this tool doesn't, you can add it — and you don't need to know C#.

The interface is plain JSON: one file per language in src/SignsOfAI.UI/wwwroot/i18n/, plus a locales.json manifest. Adding a language is copy en.json, translate the values on the right, add one line to the manifest. No build step, no code to read, and the language switch picks it up on its own.

You don't have to finish. Any key you leave out falls back to English, so a partial translation ships as partly translated rather than as a page full of blanks — translate the navigation and the main page, open the pull request, come back for the rest whenever. Contributors are credited on the switch itself.

Every pull request runs a set of locale tests that name the exact mistake — a mistyped key, a duplicated entry, a lost {0} placeholder — so a translation can be reviewed on evidence instead of by reading JSON side by side. They deliberately do not fail for an incomplete translation.

Full guide → Docs/TRANSLATING.md

Deploy

The Blazor client is a static bundle (hosts anywhere free). Included GitHub Actions:

• GitHub Pages (deploy-pages.yml) — Settings → Pages → Source: "GitHub Actions". The workflow rewrites the base href and writes an SPA 404.html fallback.

• Azure Static Web Apps (azure-static-web-apps.yml) — add the deployment token as a repo secret.

The optional server is a normal ASP.NET Core app (dotnet publish the SignsOfAI.Perplexity.Api project).

Credits

Created by Pedro Hernández — PeopleWorks, Microsoft MVP for .NET. Detection markers are grounded in linguistics research on AI stylometry — see Docs/GoogleResearch.md.

The chat.* rules — the assistant's own turn, left in the document — were adapted from the pattern set of amanmaqsood/prose-humanizer (MIT), a writing skill rather than a detector. They entered the packs the way everything here does: screened against the calibration corpus first, where all six scored zero. Twelve other candidates from the same source did not enter, because they fire on writing from before 2022.