eula-diff

Compare two versions of a EULA or privacy policy and see what actually changed — a clause-level redline instead of a noisy line diff, so reflow, renumbering, and moved sections don't drown out the substance.

eula-diff is a small, deterministic Go tool: it extracts, normalizes, segments into clauses, aligns the two versions, and emits a structured redline (text or JSON). It ships with a companion Claude skill that reads the JSON and adds the semantic layer — classifying each change and calling out who it favors.

Why not just diff?

Two revisions of the same agreement rarely line up textually. A paragraph rewraps and every line reads as changed; inserting one section renumbers all the rest; an arbitration clause moves from §12 to §3. A line diff screams at noise and buries the one edit that matters. eula-diff aligns clauses, not lines, so cosmetic churn falls away and real changes stand out.

Install

go install github.com/husobee/eula-diff/cmd/eula-diff@latest

Or build from a checkout:

go build -o eula-diff ./cmd/eula-diff

Usage

eula-diff [--json] <old> <new>
eula-diff --text <file>

• <old>, <new> — the two versions as .txt, .md, or .html files (convert PDFs to text first, e.g. with pdftotext).
• --json — emit the structured diff instead of the human summary.
• --text — print the cleaned, normalized text of a single file (the input the segmenter sees). Use it to re-analyze raw text when confidence is low.
• --version — print the version.

Segmentation confidence

Clause splitting is heuristic and does not cope with every layout, so each run reports a confidence level (high / medium / low). When it isn't high — typically because a document collapsed into a single clause — the clause-level diff is unreliable and should be treated as such; the human summary prints a warning, and the companion skill falls back to --text and re-reads the prose.

Human summary:

$ eula-diff testdata/privacy_v1.txt testdata/privacy_v2.txt
testdata/privacy_v1.txt -> testdata/privacy_v2.txt
7 -> 7 clauses | +1 added  -1 removed  ~3 modified  >1 moved  =2 unchanged

[MODIFIED] 1 Information We Collect
[MODIFIED] 3 Data Retention
[MOVED] 4 Your Rights
[MODIFIED] 5 Third Parties
[ADDED] 6 Security
[REMOVED] 3 Cookies

Structured diff (--json) reports each change with a word-level redline:

{
  "status": "modified",
  "v1": { "number": "3", "heading": "Data Retention" },
  "v2": { "number": "3", "heading": "Data Retention" },
  "similarity": 0.68,
  "redline": [
    { "op": "eq",  "text": "We retain your personal data for " },
    { "op": "del", "text": "12 months after account closure." },
    { "op": "ins", "text": "as long as your account is active." }
  ]
}

Pipeline

 old file ─┐
           ├─►  extract ─► normalize ─► segment ─► align ─► redline ─► report (text | JSON)
 new file ─┘

• extract — .txt / .md as-is, .html reduced to visible text.
• normalize — unify glyphs and whitespace, de-hyphenate line breaks, strip page furniture.
• segment — split into clauses on numbered / labeled / all-caps headings.
• align — match clauses across versions by content similarity; classify each as added, removed, modified, moved, or unchanged.
• redline — word-level LCS diff for modified clauses.
• report — assemble the JSON contract (or a terse terminal summary).

Claude skill

skill/ is a Claude skill that runs eula-diff --json and turns the structured diff into a plain-language review: each change tagged by category, direction (favors user / vendor / neutral), and severity, with the red flags (added arbitration, indefinite retention, enabled data sale, removed opt-outs…) surfaced first. See skill/assets/example-report.md for a worked example. To use it locally, symlink or copy skill/ to ~/.claude/skills/eula-diff/ and put eula-diff on your PATH.

The tool is deterministic and testable; the semantic judgment lives in the skill. It is a drafting aid, not legal advice.

Development

go test ./...                       # run the suite
go test ./internal/cli -update      # regenerate golden fixtures

License

MIT — see LICENSE.