Prompt Version Diff

Version A (Before)
Version B (After)

Prompt-Specific Highlighting

varVariable changes

{{var}}, {var}, $var, ${var}

xmlXML tag changes

<tag>, </tag>, <self-closing/>

instructionInstruction keywords

must, never, always, do not, required...

What This Tool Does

Prompt Version Diff is built for deterministic developer and agent workflows.

Compare two prompt versions with diff highlighting. Detects variable changes, XML tags, instruction keywords, and token count delta.

Use How to Use for execution steps and FAQ for constraints, policies, and edge cases.

Last updated:

This tool is provided as-is for convenience. Output should be verified before use in any production or critical context.

Agent Invocation

Best Path For Builders

Browser workflow

Runs instantly in the browser with private local processing and copy/export-ready output.

Browser Workflow

This tool is optimized for instant in-browser execution with local data handling. Run it here and copy/export the output directly.

/prompt-version-diff/

For automation planning, fetch the canonical contract at /api/tool/prompt-version-diff.json.

How to Use Prompt Version Diff

  1. 1

    Compare two AI prompt versions line-by-line

    Paste old prompt in left panel, new prompt in right panel. The tool highlights additions (green), deletions (red), and changed sections. Identify exactly what changed in your system prompt.

  2. 2

    Track prompt iteration for A/B testing

    Before running A/B test, document both prompts with the diff tool. Shows semantic changes (new instructions, removed constraints). When results differ, you know which changes caused it.

  3. 3

    Semantic diff: understand intent changes

    Unlike text diff, semantic diff groups logically related changes. If you rewrote a constraint three different ways, semantic diff shows 'constraint changed' not three individual edits. Clearer story.

  4. 4

    Audit prompt history for unintended creep

    Compare original system prompt to current version. Semantic diff reveals if prompt has accumulated conflicting instructions or scope creep. Useful before production deployment.

  5. 5

    Document safety/guardrail changes

    If adding safety constraints to a prompt, use diff to highlight new guardrails. Archive the diff for compliance/audit logs. Shows exact when safety measures were introduced.

Frequently Asked Questions

Why not use a regular diff tool for prompts?
Regular diff tools miss prompt-specific changes like variable additions ({{new_var}}), XML tag restructuring (<system>/<context>), and behavioral instruction modifications (changes to 'must', 'never', 'always' rules).
What prompt variable formats are detected?
The tool detects {{variable}}, {variable}, $variable, and ${variable} patterns. It tracks additions, removals, and renames of variables across both prompt versions.
Does this tool track behavioral changes?
Yes, it flags changes to instruction keywords like 'must', 'never', 'always', 'do not', 'ensure', and 'avoid' as behavioral modifications — highlighting where the prompt's constraints changed.
Can I see token count differences?
Yes, each version shows its estimated token count with the delta highlighted. This helps you track prompt size growth across iterations.
Is this tool free and private?
Free to use. Your prompts are processed entirely in your browser and not sent to external servers. All diff computation happens client-side.