Why compare prompts by token, not word?

Tokens are what you pay for and what fills the context window; a small wording change can add many tokens if it introduces rare words or punctuation.

What do the ignore options do?

They normalise case, collapse whitespace or strip punctuation before diffing, so you only see the changes that matter semantically.

Can I diff long system prompts?

Yes. Word and line modes handle long prompts comfortably; character mode is best for short strings.

Is anything uploaded?

No. Both prompts and the tokenizer run entirely in your browser.

Does it work offline and on mobile?

Yes. Once the page has loaded it keeps working without a network connection, and the layout is responsive so it stays usable on phones and tablets.

Prompt Diff & Compare

Compare two prompt versions word by word with a token delta.

Works Offline

Privacy First

No Login

No API

Compare by

Encoding

Ignore case

Ignore whitespace

Ignore punctuation

Similarity

57.0%

Added chars

Removed chars

Token delta

Prompt A — 24 tokens

Prompt B — 30 tokens

Inline diff

You are aan helpfulexpert research assistant. Answer the question using only the provided context.
Be concise.concise and cite sources.

About the Prompt Diff & Compare

See exactly what changed between two prompt revisions: word, line or character level diffs, similarity score, added and removed characters, and the exact token delta using real BPE tables so you know what the edit costs per call.

Examples

Prompt revision

helpful assistant vs expert research assistant

Output

92.4% similar, +7 tokens

Keyboard shortcuts

Copy the main outputCtrl / ⌘ + Shift + C
Download the resultCtrl / ⌘ + S
Share this toolCtrl / ⌘ + Shift + S
Reset the inputsAlt + R
Open the tool search paletteCtrl / ⌘ + K

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Frequently asked questions

Version 1.0.0 · Updated 2026-08-15 · Runs entirely in your browser