Free
One check comes back every 16 hours 48 minutes, so an empty bank is full again in a week. No account.
10 checks
See what’s hidden before you paste.
Check copied text and files for hidden instructions before they reach your AI.
Document
Paste text, drop a document or choose a file. It stays in this browser tab.
⤓Drop a documentPDF, HTML, or image · up to the browser limit
Edit pasted text
Or drop a PDF, image, HTML or text file here.
Try free
Review
Review clues, not a safety verdict
What we check
Tiny or faint textWords that are very small, transparent or close to the page colour.
- Very small textText far smaller than the document's ordinary body text.
- Text that blends into a flat backgroundTransparent text, or text whose colour is nearly the same as a flat surface behind it.
Hidden or covered textWords hidden by layout, outside the page, covered by other content or without visible marks.
- Hidden HTML or off-page PDF textHTML text hidden by layout, clipping, or zero-size containers; PDF text outside the page or without visible area.
- HTML text covered by another elementRendered text whose location is covered by an opaque component or overlay.
- PDF text with little or no matching visible imageExtractable PDF text without clear visible marks in a flat or solid rendered page region.
- PDF text beneath an opaque painted areaExtractable PDF text occupying the same region as an apparently solid painted area.
Invisible or unusual charactersCharacters you cannot see, changes in reading order, and letters that resemble other letters.
- Invisible and control charactersInvisible characters, Unicode tags, variation selectors, and reading-order controls in extracted text.
- Mixed scripts and character variantsMixed Latin/Greek/Cyrillic words and compatibility variants such as fullwidth letters. Not a complete lookalike check.
Encoded textCharacter codes and encoded blocks that can contain readable words.
- Escaped character codesRuns of three or more hexadecimal, Unicode, or percent escapes in extracted text. ASCII art and arbitrary encodings are not decoded.
- Readable encoded textUnicode tags, zero-width binary, variation-selector bytes, escapes, readable Base64 and hex. At most three passes and forty candidates per source; not all encodings.
Instructions to an AIEnglish patterns asking an assistant to change tasks, reveal information or take action.
- Instructions aimed at an assistantEnglish patterns for task changes and claimed authority. Quotations and training examples can match.
- Requests to disclose data or actEnglish patterns for disclosure, external destinations, commands, and record changes.
Extra document contentWords in comments, document fields and other content outside the main text.
- Clues in extra document fieldsSupported HTML attributes, comments and inert content; PDF metadata, annotations and fields. Embedded files are not opened.
PDF text differencesCopied text can differ from words read from the page image. Text recognition errors can cause this too.
- PDF text and OCR disagreementCompare extractable text with independently read page pixels. OCR errors can cause disagreement.
Matches need context. No findings does not establish that a document is safe.
10 of 10 free checks left
Your text stays in this browser tab. Nothing is uploaded.
Chrome extension coming soon
What prePaste does
Shows what you can’t see
White text, tiny text, text pushed off the page and invisible characters, pulled into plain view.
A full review before you send
See the document beside its findings. Read what was hidden, then choose the text you want to use.
Stays in your browser
The check runs on your device. No account, no upload.
Open the file. Read the full story.
Choose a file above, then open Review results. Read what was found and edit the text you want to use.
Keep the original file. Copy your reviewed text or download it as a .txt file.
How it works
Open a file or paste
Choose a PDF, image, HTML or text file. Or copy straight from a document and paste it here with its formatting.
Review the results
See each finding beside the document, with the words and the reason they were marked.
Choose what you send
Edit the reviewed text, then copy it or download a .txt file. Your original file stays unchanged.
Original assignment
MATH 101 · Practice 4
Show each step. Check your answer by substitution.
1. Linear equations 4 marks
Solve 3x + 7 = 22. Show your work.
2. Explain why the same operation must be applied to both sides.
An assignment can carry more than the question.
What it looks for
- Text the same colour as the page
- Text too small to read
- Text hidden, covered or pushed out of view
- Invisible and lookalike characters
- Encoded text that decodes to words
- Words that give an AI new instructions
prePaste runs a fixed list of checks. The instruction check reads English. A clean result means nothing matched, not that the text is safe. prePaste loads nothing your text points to, so a web address written inside it can be left out of what is shown.
Pricing
Lifetime
Unlimited prompt injection checks. Pay once and we’ll email your activation key.
$79.00 once
USD. Lifetime access. No renewal payments.
First 100 purchases: 50% off ($39.50). Purchases 101–1,000: 25% off ($59.25).
Limited to the first 1,000 purchases.
Privacy
The check runs in your browser tab. Your text is not sent to prePaste or anywhere else.
Your free-check count stays in this browser. You can check text without an account.
Stripe handles payment and billing. prePaste and its mail provider use your checkout email to send your activation key. prePaste receives that key when you activate access or open billing. Activating also sends this browser’s public key. This browser saves a lifetime key to refresh access automatically. Your pasted text stays here.
Questions
- Does a clean result mean the text is safe?
- No. prePaste runs a fixed list of checks and shows you what they find. Nothing found means nothing matched those checks.
- Why paste instead of retyping?
- Hidden text is hidden by its formatting: its colour, its size, where it sits. Copying from the document keeps that formatting. Retyping loses it.
- Who is it for?
- Anyone who pastes text they did not write into an AI: an assignment, a PDF, a web page, an email.
- What counts as one check?
- Each file or paste you check is one. Opening its review and editing or copying the reviewed text use no extra checks. All three homework examples on this page are free.