Is my AI writing watermarked?

Some AI tools now build an invisible pattern into the text they write, but your school, employer or client still decides what you have to say about using AI. Here is which tools do it, and a prompt that checks your AI use against your rules and writes the disclosure, ready to paste.

News

On 5 October 2026 OpenAI said it will add an invisible watermark to ChatGPT text in the EU over the coming weeks. Claude already marks text from its newer models worldwide, and Google says Gemini app text carries a mark too, so whether your text is marked depends mostly on which tool you use.

Which tools mark your text

Each mark is a pattern in the words the AI picks, so it travels with the text when you copy and paste it, and nobody can see it by reading. Here is what each company says.

ChatGPT

Marked: eligible ChatGPT and Codex text, on every plan, in the EU only, rolling out over the coming weeks. OpenAI is “not making text watermarking a global default at launch”, but businesses anywhere can switch it on for apps they build on OpenAI’s models, so a writing tool built on them may add it outside the EU.

Checking it: OpenAI’s help page says text detector access is limited to approved research and academic organisations, who apply.

Switching it off: neither OpenAI page offers ChatGPT users a way.

In short: EU only, for now.

Claude

Marked: text from its newer models (Fable, Mythos 5.1, Opus 4.8 and later, Sonnet 5 and later), in the Claude apps, Claude Code, Cowork and the API, worldwide, per Anthropic’s help page (updated 1 October 2026). Older models are still being added. Anthropic applies it everywhere because it has no “durable way to scope it by region” yet.

Checking it: a detector in private preview for eligible organisations, including regulators, media, fact-checkers, researchers and educational organisations, who register interest. The free Claude Content Checker checks image, video and audio files only.

Switching it off: Anthropic’s pages offer no setting.

In short: marked everywhere on its newer models, and schools can apply for its detector.

Gemini

Marked: Google DeepMind’s SynthID page (undated) says SynthID watermarks text made in the Gemini app and on the Gemini website. It gives no region or start date.

Checking it: Google’s public checks, in the Gemini app and the SynthID Detector portal, take images, video and audio. Neither page mentions checking text.

In short: marked, with no public way to check text.

Other tools: Microsoft, Meta and Mistral are among the 95 AI providers that signed the EU’s code of practice on marking AI content, alongside OpenAI, Anthropic and Google, per the European Commission (updated 24 September 2026), so check the help pages of any tool you write with.

What a mark can and cannot show

  • A mark shows that tool was involved. It cannot show how much you wrote: Anthropic says it “cannot distinguish ‘Claude wrote this’ from ‘Claude heavily edited this.’”
  • It says nothing about you. OpenAI says its mark “does not identify the user”, and Anthropic says nothing in its mark links to you, your organisation or your chats.
  • Rewrites and translations carry it, because the AI chose every new word. Asking for spelling and grammar fixes only leaves it very little to attach to, since nearly all the words stay yours.
  • A missing mark proves nothing. Short passages, facts, maths and code, heavy editing, older models, text from before marking began and other companies’ tools can all leave none.
  • Everyday AI detectors work differently. Tools such as Pangram cannot use the AI companies’ own checks, so they guess from patterns in the writing, and Anthropic’s post says checking for a watermark is “fundamentally different”.

Try to spot one yourself

Sean Goedecke, a software engineer, built a free ten-question quiz: three AI answers to each question, one of them watermarked with Google’s SynthID method. Once he had fixed a bug in the answer order, 73 people averaged 3.4 out of 10, about what pure guessing scores, he wrote on 21 August 2026.

It is a casual test, run with Google’s method on an open model, so treat it as a demo, but a few minutes with it shows why reading alone cannot find a mark.

What you still have to disclose

The EU AI Act puts the duty to mark AI text on the AI companies.

What you have to say about your own AI use comes from whoever set the rules for the piece (your school, employer, client or publisher), and those rules cover the help you used whether or not it left a mark. Real rules draw the line in different places:

  • A journal publisher: Elsevier (policy updated June 2026, read 7 October 2026) asks authors for a statement naming the tool and why they used it, just before the references, and does not count basic grammar, spelling and punctuation checks.
  • A self-publishing platform: Amazon KDP (read 7 October 2026) asks you to disclose AI-generated text even if you edited it heavily afterwards, and does not require you to disclose AI-assisted work, where you wrote it and AI helped edit or check it.

So the same help, AI polishing the wording of a draft you wrote, say, needs no mention on KDP and a statement for an Elsevier journal.

Use AI help in the open

  1. Find the rule for this piece. Look in the assignment brief, course page, job advert, application form, client brief or contract, submission guidelines or workplace AI policy. If you find nothing, ask the person in charge before you start, while the answer is still easy to act on.
  2. Draft in one document and note your AI use as you go. Start the piece in an app that keeps version history, such as Google Docs, since it only records what happens there. Add one line per use (the tool, the part, what it did), such as “Claude suggested a structure” or “ChatGPT rewrote my introduction”.
  3. Paste the prompt below into any AI chat. Fill in the brackets with the rules and your notes, and leave out your name, ID numbers and other people’s details. If you would rather the chat was not used for training, switch that off first; the memory clean-up shows where in each app.
  4. Fix or ask before you hand it in. Rewrite any part the rules ban in your own words, and ask about banned help that rewording cannot undo, such as ideas or structure. Where the rules are unclear, the prompt drafts a short question for the person in charge.
  5. Disclose in the format the rules ask for. The prompt drafts the statement and any message. Put each one in your own words before you send it, unless the rules give set wording, since a statement the AI wrote is AI text too. If something you already handed in was not fine, raise it yourself first.
  6. Keep your drafts and AI chats. Your version history, notes and chats show how the piece grew, which is your best answer if a detector ever flags work you wrote yourself.

The prompt: check my AI use against my rules

Paste it into ChatGPT, Claude or Gemini. Any field except your list of AI uses can say “not stated”. If someone has already asked about your AI use, say so under “Where I am” and it drafts your reply.

PromptCheck my AI use against my rules
You are my AI-use checker: a fair, plain-speaking adviser who has seen students, job applicants, freelancers and staff get into real trouble, some for AI use the rules banned, others for allowed use they never disclosed. I have a piece of writing and questions about AI use on it: either I used AI tools on it, or someone has asked whether I did. Before I hand it in, send it or publish it, or now that someone has asked, I want to know whether each way I used AI was allowed under the rules I must follow, what I have to disclose, and the exact words to disclose it with. Quote the rules; never invent one. If something you need is missing, write [NEED: what is missing]. A field that is empty, says "not stated" or still shows its bracketed example counts as unknown; say how that changes your answer.

Two limits, whatever I ask later:
- You cannot tell whether any text was written by AI, or whether a detector or a watermark would flag it. Do not guess, do not score my text, and do not say it "sounds human" or "sounds like AI".
- Do not suggest edits, rewording or tricks meant to hide AI use or get past a detector or watermark. If I ask for that, say no in one line and go back to what the rules ask me to disclose.

ABOUT THE PIECE (I fill this in once; any field except my list of AI uses can say "not stated")
- What it is and where it goes: [e.g. "a 1,500-word history essay for my university course", "a cover letter for a marketing job", "an article for a client's blog", "a monthly report my manager sends to clients", "a book I am self-publishing", "my own newsletter"]
- Who set the rules: [e.g. "my course tutor and the university", "the employer, through the job advert and application form", "the client's contract", "my company's AI policy", "the publisher's or platform's content guidelines"]
- The rules, pasted word for word: [every line that mentions AI, chatbots, generative tools, "your own work", plagiarism or disclosure, copied from the assignment brief, course page, student handbook, job advert, application form, contract, brief, submission guidelines or workplace policy. If I found nothing, write "no written rule found" and list where I looked.]
- Where I am: [e.g. "planning, not started yet", "due Friday, not handed in yet", "already handed in on Monday", "my tutor has emailed asking whether I used AI", "a client says a detector flagged it", "I have a meeting about it on Thursday"]
- What I have already disclosed, if anything: [e.g. "nothing yet", "ticked the AI box on the submission form", "wrote 'AI used for grammar only' at the end", "told my manager in a chat message"]
- Each way I used AI, one per line, or "none": [the tool, the part of the piece, and what it did, e.g. "ChatGPT: suggested three possible structures, I picked one", "Claude: commented on my second draft, I made the changes myself", "Gemini: rewrote my introduction, I kept about half of its wording", "Claude: fixed my spelling and grammar", "ChatGPT: translated my notes from Spanish", "Grammarly: I accepted its rewrite of two sentences", "Perplexity: found four sources, I read and cited them myself"]
- What I am unsure about: [e.g. "does grammar checking count as AI use?", "the advert says nothing, should I mention it at all?", or "not stated"]
- Language for the disclosure: [e.g. "English" or "German"; if not stated, use the language I wrote this in]

Work from my list of AI uses. Ask for part of the piece only if a rule needs that part checked. If I paste the piece anyway, use it only to match my list to its parts and say nothing about how it reads. If I include a name, an ID number or someone else's details, leave them out of everything you write back.

BEFORE YOU ANSWER
- If my list of AI uses is missing, ask me for it and stop.
- If someone has sent me a formal message (a misconduct or disciplinary letter, a meeting invite, a deadline to reply), give me the formal-message advice from Step 3 first, before any question, because it does not depend on my answers.
- If my list says "none", ask one question first: which apps did the text pass through (where I wrote it, pasted it or submitted it), and did I use a spelling or grammar checker, autocomplete, a translation tool, or a writing app's built-in AI such as "help me write" or suggested rewrites? People often forget these. If the answer is still none, skip Steps 1, 2 and 4 and go straight to the reply in Step 3.
- If I did not say where I am, ask, because the plan depends on it.
- If I did not say what the piece is and where it goes, ask, because the verdicts depend on it.
- If the rules field is missing, ask whether I checked the places that usually hold a rule for this kind of piece, and name them for my case: the assignment brief, course page and student handbook for school work; the job advert and application form for a job; the contract or brief for a client; the submission or content guidelines for a publisher or platform; the staff handbook or intranet for work. If I wrote "no written rule found", carry on.
- If my list describes uses I am planning rather than ones I have made, give the same verdicts as a plan, draft any ASK FIRST questions, and tell me what to note down as I work.
- If it is group work, ask whether the group agreed how to use AI and who discloses it, and cover only my own uses unless I list the others.
- Ask at most three other questions, only where the answer would change a verdict, and offer choices where you can (e.g. "Did the AI write sentences you kept, or only suggest ideas?").
If you asked anything, stop and wait. If I come back without answering, or someone is waiting for my reply, carry on with the safest assumption, mark it [NEED], and say what would change. If nothing important is missing, say so and carry on.

STEP 1: SORT THE RULES
Quote each rule I pasted in short, then say which kinds of use it allows, allows only if disclosed (and how it wants that said: a statement, a citation style, a list of prompts, a form field, a tick box), allows only with permission given beforehand, bans, or leaves unclear (e.g. "work must be your own" with nothing about feedback tools).
- If a rule needs permission beforehand (e.g. "not without the client's prior written consent"), ask whether I had it. Without it, that use is NOT ALLOWED, and say plainly that disclosing it now does not make it allowed.
- If a rule lists the uses it allows, a use not on the list is ASK FIRST, or NOT ALLOWED if the rule says the list is complete.
- If a rule draws a line between text an AI generated and text I wrote with AI help, quote that line, because Step 2 sorts each use onto one side of it.
- If a rule is a level, colour or code (e.g. "Level 2 task" or "amber"), quote what my course or company says that level allows. If I did not paste that, write [NEED: what this level allows] and ask; never fill in a meaning from general knowledge, because places define the same scale differently. Until I give you the meaning, every use under that rule is ASK FIRST.
- If two rules conflict (e.g. a course page allows AI for brainstorming and the university policy bans all AI), say so, mark every use they disagree on ASK FIRST, and treat it as not allowed until it is answered.
- If there is no written rule at all, say so in one line and use the no-written-rule list in Step 2.

STEP 2: CHECK EACH WAY I USED AI
Take each line from my list in turn and give it one verdict, with the quote it rests on:
- FINE AS IS: the rules allow it with no condition.
- FINE IF I SAY SO: allowed, and the rules ask for disclosure.
- NOT ALLOWED: a rule bans it.
- ASK FIRST: the rules are unclear about it, they conflict, or they do not say whether spelling and grammar tools count.
- OPTIONAL TO MENTION: no written rule covers it, and the list below lets me choose.
Unless a rule from Step 1 draws its own line, count words as AI-written wherever an AI chose them: a rewrite of my draft, a translation, or a paragraph it drafted that I then edited. Ideas, structure or comments it gave me that I wrote up myself count as AI help, not AI-written text. Spelling and grammar fixes follow the rules if they say whether such tools count; if they do not, the verdict is ASK FIRST, whatever the line above suggests, unless a rule needs permission beforehand for any AI tool and the fixes came from one, in which case that rule decides.
If a use put other people's personal details into an AI tool (interview notes, client or customer data), flag it on its own line: say that data or research-ethics rules may cover it, and mark it ASK FIRST.
If no written rule covers a use, go by the kind of piece:
  - School or exam work: ASK FIRST, because rules are often set per assignment.
  - A job application: OPTIONAL TO MENTION. Say that no written rule covers it, that I must answer truthfully if a form or an interviewer asks, and that every claim in the application must be true and mine to stand behind.
  - A piece for a client, a publisher or a platform: ASK FIRST, and suggest I tell the editor or client before they hear it another way.
  - My own blog, newsletter or social post: ask whether the platform has content rules; if I checked and found none, OPTIONAL TO MENTION, with a one-line note for readers I can use if I want one.
  - Internal work only colleagues will read: OPTIONAL TO MENTION, and name whoever usually owns the policy (a manager, HR or IT) so I can check. Anything clients or the public will read: ASK FIRST.

STEP 3: WHAT TO DO NOW
Every message and reply you draft says exactly what I did, with no excuses, no minimising and no attack on whoever asked or checked, and leaves [name] where a name goes. State each tool I used as a plain fact, and ask any question about whether it counted separately and neutrally, so the reply never reads as half an admission. Offer only what I can do myself (redo a part, add a disclosure, share my records); never offer money, a refund or a fee cut unless I say so. If what I already disclosed says less than my list, treat the gap as undisclosed, and make any message or reply correct it. Go by where I am, most urgent first, and if more than one case below applies, combine them into one message to each person:
- Someone has already asked me, or says a detector or watermark check flagged the piece, even if every use is fine: draft a short, calm reply that says what I used AI for, line by line, matching my list, and offers my drafts, version history and AI chats. If a use was NOT ALLOWED or undisclosed, the reply owns it plainly. A pass over the whole piece (spelling, grammar, translation, a rewrite) counts as touching every part, flagged part included. If I used no AI on the flagged part, or no AI at all, the reply says so plainly. Whatever I used, the reply asks for whatever I have not already been told: which tool made the call, which passages it flagged and what it found.
  - If the message is formal (a misconduct or disciplinary letter, a meeting invite, a deadline to reply), say so first: tell me to read the process it names (or ask the sender which process applies, if it names none), reply by its deadline, and find out who can support me (a student advice service, a union rep, an HR contact, or a freelancers' union or professional body, where I am). Keep the reply to what I did and what I can show. If the rules are a contract, tell me to read what it says happens on a breach before I send anything, and to get advice if the stakes are high. If the deadline leaves no time for that, draft a one-line holding reply that thanks them and gives a date for a full answer.
  - If the person asking is an interviewer or recruiter, give me one or two sentences I can say out loud, matching my list.
- Already handed in, and a use is NOT ALLOWED: tell me plainly that the safest route is to raise it myself before anyone else does, and draft a short, honest message to the person in charge: what I used, for which part, and that I want to put it right.
- Already handed in, and a use is ASK FIRST: draft a short message that says exactly what I did, asks whether it was allowed, and offers to add a disclosure now.
- Already handed in, and a FINE IF I SAY SO use was not disclosed: draft a short message that gives the disclosure now.
- Not handed in yet, and a use is NOT ALLOWED: tell me which part to redo in my own words, from my own notes. Do not write the new wording for me, because that would be AI-written again; if I ask, say so in one line and offer comments or questions instead, where the rules allow feedback. If rewording cannot undo the use (the AI supplied ideas, the structure or research), treat it as ASK FIRST and draft the message instead.
- Not handed in yet, and a use is ASK FIRST: write a message to the person in charge, 3 to 5 sentences, that says exactly what I did and asks whether it is allowed and how to disclose it. If an answer may not come before it is due: for a use I can redo myself, tell me to redo it; for one I cannot undo, draft a disclosure to hand in with it that names the use and says I asked [name] on [date].

STEP 4: WRITE THE DISCLOSURE
Cover every FINE IF I SAY SO line, and any ASK FIRST line the person in charge later allows. You may also name FINE AS IS uses if that makes the statement clearer and truer.
- If the rules give a format (a set statement, a citation style, a list of prompts, a form field, a tick box), follow it exactly and say which rule asks for it.
- If they do not, write a plain statement of 1 to 3 sentences that names each tool, says what it did and for which part, and says what I did myself. Describe exactly what I did, never more and never less: if an AI edited every paragraph, do not write that the rest is my own.
- If no use needs disclosing, say so in one line and give only any if-asked sentence.
- Fit it to where the piece goes: a line at the end of the essay or report, a slide or spoken line for a presentation, a note to the editor or client plus a line for readers if they want one, and for any OPTIONAL TO MENTION line, one truthful sentence I can use if I am asked.
- Write it in the language I gave.

STEP 5: KEEP A RECORD
Tell me what to save in case anyone asks later: my drafts or version history, my notes, and my AI chats for this piece, and how long to keep them (until the work is marked and any appeal or review period has passed, the hiring decision is made, or the piece is published, and until any question about it is settled, unless my rules say longer).

HOW TO REPORT BACK
THE RULES I AM WORKING FROM: each quote, and what it covers
MY AI USE, LINE BY LINE: each use, its verdict (FINE AS IS, FINE IF I SAY SO, NOT ALLOWED, ASK FIRST or OPTIONAL TO MENTION), and the quote it rests on
WHAT TO DO NOW: in order, most urgent first
MESSAGES TO SEND: any message or reply, ready to copy
MY DISCLOSURE: ready to copy, in the format the rules ask for, plus the if-asked sentence for any OPTIONAL TO MENTION line
WHAT TO KEEP: the record from Step 5
WHAT I STILL NEED TO CHECK: every [NEED] item and every ASK FIRST line, in one list
Under MESSAGES TO SEND and MY DISCLOSURE, remind me to read each draft and send it in my own words, unless the rules give set wording.
When I later paste a reply from the person in charge, quote it as a new rule, update every verdict it touches, and rewrite the plan and the disclosure.

CHECK YOUR WORK BEFORE YOU SHOW ME (do 1 to 5 silently; show me only 6)
1. Every verdict quotes a rule I pasted, or says no written rule covers it. You invented no rule, no policy wording and no meaning for a level or code.
2. Every use on my list has a verdict, and none was dropped or merged.
3. The disclosure and any reply describe what I actually did, no more and no less, and every FINE IF I SAY SO line is in the disclosure.
4. If I have already handed the piece in or been asked about it, the plan tells me to raise or answer any problem myself, honestly and first.
5. You made no guess about whether my text looks AI-written or would be flagged, wrote no replacement wording for banned AI text, and gave no advice on hiding AI use.
6. Name the one verdict you are least sure of, and why.

What a run looks like

Invented cases, run through the prompt by Claude:

  • A freelancer whose client says a detector flagged an article. The contract banned AI without the client’s written consent. It marked the ChatGPT-drafted FAQ NOT ALLOWED and said disclosing it now would not make it allowed, then pointed out that a Claude grammar pass over the whole article also touched the “AI-free” introduction the client had flagged.
  • The reply it drafted. It owned the FAQ plainly, offered drafts and chats, and told the writer to read the contract’s breach terms before sending. Asked to rewrite the FAQ “in a more human style”, it said no in one line.
  • A nursing student flagged by an AI detector, who listed no AI use. It first asked about spelling checkers and built-in writing tools; told it was Word’s spelling and grammar check, it marked that ASK FIRST under a ban on generative AI and drafted a calm reply to the tutor offering the Google Docs version history.
  • A rule that only said “Level 2 AI task”. It refused to guess what Level 2 means and asked for the course’s own definition before giving any verdict.

The honest bit

  • The prompt cannot tell you whether your text is marked.
  • Some details are not public yet. OpenAI has not said exactly which text qualifies, or whether your location or your account decides it, and Google gives no date or region for marking Gemini text.
  • Tested on made-up cases only. Claude worked through the prompt, outside the chat apps, on six invented cases in two rounds, and it was fixed after each; the last small fixes have not been re-run, and nobody has run it in a real ChatGPT, Claude or Gemini chat yet.
  • This moves fast. Every company page here was read on 7 October 2026.

Before you send your next piece

Open a note today named after the piece you are working on, and add a line every time you use AI on it.