Short answer: ordinary users currently have no public OpenAI tool for checking whether text contains OpenAI’s invisible watermark. OpenAI’s text detector is restricted to approved researchers and expert organizations that apply for access. The public verifier and Content Provenance API support images and audio, not ordinary text. And even an authorized detector’s result is evidence about provenance—not proof of authorship.
What OpenAI’s invisible text watermark is
OpenAI calls its text-watermarking method textGrain. It subtly shifts a model’s choices among possible words or word pieces, creating a statistical pattern that a detector with the corresponding secret key and settings can check. The signal is in the wording choices themselves, not in a hidden character or formatting artifact. OpenAI says textGrain does not add hidden characters, invisible spaces, extra watermark-only tokens, or unusual punctuation. (OpenAI Help Center)
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That means inspecting Unicode characters, turning on “show invisibles” in an editor, or copying and pasting text will not reveal the watermark. TextGrain is also distinct from file metadata: the signal is associated with word choices rather than a document property.
The Tool Desk
Outbyte Driver Updater FREEFix the driver behind crashes, sound loss and screen glitchesFind Drivers →Outbyte PC Repair FREERepair Windows errors before they cause bigger problemsFix Now →Not all ChatGPT text should be assumed to carry this signal. In an October 5, 2026 update, OpenAI said API customers worldwide can opt in to text watermarking for select models, with the feature off by default in the API. Eligible ChatGPT and Codex text output in the EU is scheduled for rollout “over the coming weeks.” Availability therefore depends on region, product, model, export path, and rollout timing. (OpenAI, “Our approach to EU text provenance rules”)
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Can you check ChatGPT text yourself?
There is no ordinary-user text upload checker from OpenAI at present. OpenAI’s public verifier and Content Provenance API check supported image and audio files. Text verification requires applying for access; OpenAI says applications are reviewed case by case and access is currently limited to approved organizations, including AI research and academic institutions. (OpenAI API documentation)
If you are not in an approved organization, none of the following is a reliable substitute for that detector:
- Looking for hidden characters: textGrain does not insert them.
- Asking ChatGPT whether it wrote the passage: OpenAI says ChatGPT does not know whether it generated a particular piece of writing and may make up an answer. (OpenAI Help Center)
- Running a third-party AI-writing classifier: these services estimate whether text appears AI-generated from linguistic patterns; they do not test for OpenAI’s textGrain signal. A classifier score is not a textGrain result.
What an authorized detector’s result can tell you
A detected watermark is a probabilistic signal that an OpenAI system likely generated or processed some of the text. It does not show that the model wrote the whole passage, identify the person who used the system, measure how much a person contributed, or establish the text’s truth, ownership, legality, disclosure obligations, or responsibility. (OpenAI, October 5, 2026)
A result with no detected watermark is inconclusive. The text may never have carried one: it might come from an unsupported model or generation path, or have been created before watermarking was available. A detector can also miss a signal in text that is too short, constrained in its wording, heavily edited, paraphrased, or translated. A negative result does not prove a person wrote the passage.
Because textGrain is encoded in word choices, copying and pasting unchanged wording is expected to preserve the signal. Substantial rewriting, paraphrasing, and translation can weaken or remove detectability; even an unchanged passage may be difficult to assess if it is short or has little flexibility in how it can be worded. (OpenAI Help Center)
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.How reliable are the published detection figures?
OpenAI’s published figures describe its own evaluations, not guaranteed performance on every real-world document. Results vary with passage length, subject matter, language, and edits.
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| OpenAI-reported evaluation | Reported result and conditions |
|---|---|
| Psychology-like content | About 80% of 200-token passages and about 95% of 400-token passages were detected at a 1% target false-positive rate. OpenAI reported substantially lower detection for mathematics, where wording is more constrained. (OpenAI, 2026) |
| Synonym replacement in 400-token passages | Detection fell from about 92% to 66% after replacing 10% of words with synonyms, and to 17% after replacing 25% of words. (OpenAI, 2026) |
| Translated EU-language prompts | In an evaluation of 500 synthetic English prompts translated into the other 23 official EU languages, detection at a 1% false-positive rate ranged from 69.0% for Spanish to 42.2% for Romanian. OpenAI says it can adjust watermark strength for languages with weaker results. (OpenAI, 2026) |
The EU AI Act Code of Practice on Transparency of AI-Generated Content does not require watermarks in outputs shorter than 200 tokens—about 150 English words—or in code snippets, according to OpenAI’s description of the code. That threshold is relevant context, not a test for whether a specific passage was watermarked. (OpenAI, 2026)
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Repair common Windows errors and clear accumulated junk for a smoother, more stable PC - no reinstall needed.Free scan · no reinstallHow to assess a claimed “ChatGPT watermark detector”
Before trusting a tool or a result, establish what it actually measures. A product described as an AI detector may classify writing style rather than detect an embedded OpenAI watermark. Ask whether the method is authorized and whether its evaluation covers text of comparable length, language, and editing history. Treat any conclusion as probabilistic evidence, not a definitive verdict about who wrote something.
If you have authorized access to OpenAI’s text detector, retain the passage and relevant context for assessment. The result can depend on length, language, wording freedom, and the extent of edits, so a score should not be interpreted without those details.
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