Prompt Diff
Compare two AI prompt versions side by side. See word-level diff, token delta, quality scores, and improvement hints — 100% in-browser.
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Prompt quality signals
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What is Prompt Diff?
Prompt Diff is a free browser-based tool that lets you compare two AI prompt versions side by side. It highlights every word that was added, changed, or removed, shows a live token count delta, and scores each prompt on clarity, specificity, structure, and efficiency — all without sending your text to any server.
Whether you are iterating on a system prompt, refining a few-shot example, or A/B testing different instruction styles, Prompt Diff makes the impact of each change immediately visible.
Features
- Word-level diff — added tokens highlighted in green, removed in red, unchanged in plain text
- Token estimate delta — see how many tokens (and therefore API cost) your revision adds or removes
- Quality signals — heuristic scores for Clarity, Specificity, Structure, and Efficiency for both prompts
- Keyword analysis — instantly spot new power words added and weak phrases removed
- Improvement hints — actionable suggestions when the revised prompt lacks structure or is too vague
- 100% client-side — your prompts never leave the browser
Why use a prompt diff tool?
Prompt engineering is an iterative process. Small wording changes can dramatically shift model behavior, token usage, and response quality. Without a visual diff it is easy to lose track of what exactly changed between iterations, especially when prompts grow long.
Prompt Diff gives you the same confidence a code diff provides for source changes — a clear, scannable record of every edit and its likely impact.
FAQ
How are tokens estimated?
The tool uses the widely-accepted approximation of 4 characters per token, which closely matches the GPT-4 BPE tokenizer for English text. For precise counts, use the AI Token Counter or the Prompt Tokenizer.
Is my prompt data sent to a server?
No. All processing — diffing, scoring, token counting — happens entirely in your browser using JavaScript. Nothing is transmitted or stored.
What do the quality scores mean?
Scores are heuristic estimates based on the presence of instructive keywords (format, step-by-step, JSON, etc.), structural cues (line breaks, colons, lists), prompt length, and lexical diversity. They are a guide, not a guarantee of model performance.
Can I compare system prompts or multi-turn prompts?
Yes — paste any text into the two fields. The tool works with system prompts, user messages, few-shot examples, or any freeform text you want to diff.