Checking is free and unlimited. Pay for the rewriting.
Everything runs on your device, so checking costs us nothing to serve and is not rationed: no account, no word cap, no monthly count. What you pay for is correction. The free plan rewrites 20,000 tokens every 7 days on the Standard engine; Pro removes that budget, adds the Pro rewrite engine, and, for checking, the server-side path: keys a browser cannot hold, a stored record, and a document you can hand to someone else.
Free
£0No account needed
- Unlimited checking, in your browser, with no account and no word limit
- 20,000 tokens of rewriting every 7 days, on the Standard engine
- Confidence band, per-passage breakdown and stated limits on screen
- Your document is never uploaded, on any feature
Pro
Most complete£19per month
- Unlimited rewriting, with no weekly token budget
- The Pro rewrite engine: a real language model in your browser, more candidates per passage, and the extended AI-tell library
- The dated evidence report as a PDF: signal strength, per-passage breakdown, stated limits, document hash
- API and MCP access to checking, metered; rewriting is always on-device, on every tier
A document, not a screen.
The free check gives you this result and deliberately leaves nothing behind. Pro turns the same measurement into a dated PDF carrying the signal strength and its band, the per-passage breakdown after correction, the keys tested, the full stated limits and a SHA-256 hash tying it to the exact file you checked.
Rewriting itself is a separate feature, always on-device, on both plans. It cannot guarantee defeating a model vendor's undisclosed watermark, on any tier, at any price.
A mark was detected under one key.
NeverPrompted open reference scheme
not a vendor key
Green-list rate
68.0%
- Expected by chance
- 50.0%
- z
- 4.37
- p (one-sided)
- 0.000006
interval 60.1% to 75.0%
Measured over 147 distinct word pairs. Repeated pairs are counted once. The thin vertical line is the rate this statistic takes when no mark is present.
The chair thanked the working group for drafting the supporting brief, which those present found clear and remarkably short.
watermark z 2.36 · p 0.0092 · style distance not computed (passage too short to measure)
The same engine, metered
The JSON API and the MCP server expose the same checking engine, metered at 2p per 1,000 words. An agent assembling a deliverable can disclose provenance before handoff rather than leaving the recipient to discover it. Rewriting has no REST endpoint by design (it is strictly on-device on every tier); call it via the MCP server or the local package/CLI, both unmetered.
Pricing questions
- What is free, and what am I paying for?
- Checking is free, unlimited and needs no account: it runs in your browser, so it costs us nothing to serve and there is no honest reason to ration it. What is metered is rewriting. The free plan gives you 20,000 tokens of rewriting every 7 days on the Standard engine. Pro removes that budget entirely and adds the Pro rewrite engine, which is a real language model running in your browser with the extended AI-tell library and more candidate rewrites per passage. For checking, Pro also adds the dated evidence report, which the free tier structurally cannot produce, since the free check runs in your browser and deliberately leaves nothing behind.
- What counts as a token?
- One word, as this product counts them, using the same tokenizer every measurement in the detector is built on. It is not an estimate of another vendor's subword count. You can reconcile it against the word count shown next to your text, and the same document costs the same on every machine. Only text you actually send through a rewrite is charged; checking, reading a result and editing text by hand cost nothing.
- Is the API billed separately from the subscription?
- Yes. Pro includes API and MCP access, and calls are metered at 2p per 1,000 words, rounded up. A document too short for a statistic to be computed still consumes one unit, because the measurement was still performed. The machine-readable version of all of this is at /pricing.json.
- Is there a discount for students?
- The free plan is intended to cover the student case: unlimited checking, and enough rewriting for an appeal or a dissertation chapter. If you need the evidence report and cost is the obstacle, write to us.