prompt-diff-lite

Line-level diff for prompt template versions — see exactly what changed between two revisions before you ship a prompt edit. LCS-based, zero dependencies.

Install

npm install prompt-diff-lite

Quick start

import { diffLines, formatDiff, summarize } from 'prompt-diff-lite';

const diff = diffLines(promptV1, promptV2);
console.log(formatDiff(diff));
// unchanged lines prefixed with a space, additions with +, removals with -

console.log(summarize(diff)); // { added: 3, removed: 1, unchanged: 12 }

Why line-level, not word-level

Prompt edits are usually restructuring at the sentence/instruction level — reordering a bullet point, adding a constraint, dropping an example — which shows up cleanly as line changes. Word-level diffing adds real complexity (and is much noisier to read) for a case where most edits are already easy to review at line granularity, so prompt-diff-lite intentionally stays at that level.

API

• diffLines(a, b) — returns a DiffLine[] ({ op: 'equal' | 'add' | 'remove', line })
• formatDiff(diff) — unified-diff-style string ( unchanged, + added, - removed)
• summarize(diff) — { added, removed, unchanged } counts

License

MIT