Prompt Diff Viewer
Compare two prompt versions and highlight exactly what changed — word by word, line by line, or character by character.
Paste prompts in both panels above — the diff will appear here in real time.
Frequently Asked Questions
What is a Prompt Diff Viewer?
The Prompt Diff Viewer compares two versions of an LLM prompt and highlights exactly what changed — added text (green) and removed text (red with strikethrough). It is designed to help you iterate on system prompts, user messages, and few-shot examples by making every change visible at a glance.
Which diff mode should I use?
Use Words mode for most prompt comparisons — it shows which individual words were added or removed and is the easiest to read. Use Lines mode when you restructure prompts paragraph by paragraph and want to see which whole lines changed. Use Chars mode only when you are making very fine-grained edits and need character-level precision.
Is my prompt content stored or uploaded anywhere?
No. All diffing runs entirely in your browser using a local JavaScript library. Your prompt text never leaves your device and is never sent to any server. The tool works offline after the initial page load.
What does the "Copy B" button do?
"Copy B" copies Version B — the revised prompt — to your clipboard, ready to paste directly into ChatGPT, Claude, Gemini, or your application code. It copies the clean text, not the diff annotations.
Can I compare system prompts, user messages, and few-shot examples?
Yes. The tool works on any text — system prompts, user turn messages, assistant responses in few-shot examples, or any other LLM input. Paste any two text blocks and it will show you the diff.
What is the maximum size prompt I can compare?
There is no hard limit — the comparison runs in your browser and is limited only by your device memory. In practice, prompts up to 50,000 characters compare instantly. Very large text blocks (500K+ characters) may cause a brief pause while the diff is computed.
How is this different from a regular text diff tool?
A general-purpose diff tool is designed for code or documents and often shows line-by-line changes in a format suited to programming. This tool is optimised for prompt text: word-level diff is the default (most useful for prose prompts), the interface is minimal to stay out of the way during rapid iteration, and the three presets show common prompt engineering workflows.