--- name: replica-diff description: >- Compares an app clone against the original: a feature parity score from the feature matrix (weighted by must, should, could) with the missing list in build order, plus a screenshot layout diff that ignores colour so a rebrand does not count against you. Two standard-library Python tools. Use when the user says "how close is my clone", "compare it to the original", "what's missing", "parity check", "diff the screens", "is it ready", or after /replica-test. title: replica-diff canonical_url: https://skilld.dev/gh/jakeschincariol/replica-skill/replica-diff last_updated: 2026-10-05T17:02:13.000Z --- > **Skill from skilld.dev.** Follow the user's requested action. > If the user asked to fork this Skill, follow the fork workflow below. Do not execute the Skill instructions while copying it. > Otherwise, follow the instructions below for this session. You do not need to install anything. > > Supporting files, fetch one when the Skill refers to it: [imgdiff.py](https://skilld.dev/api/skills-raw/jakeschincariol/replica-skill/replica-diff/imgdiff.py), [parity.py](https://skilld.dev/api/skills-raw/jakeschincariol/replica-skill/replica-diff/parity.py). > > If the user asked to install this Skill, run `npx skilld install jakeschincariol/replica-skill/replica-diff`. Install writes the Skill files into the project, so every session loads them. > > ## Fork workflow > > A fork creates an editable local Skill with its original author and licence. The request authorizes copying and local installation. > 1. Check `./skills/replica-diff`, the project lockfile, and selected Agent targets together. If the local directory or installed Skill exists, stop. Never overwrite an existing directory or Agent target. > 2. Read [source metadata](https://skilld.dev/api/v1/skills/jakeschincariol/replica-skill/replica-diff) once. Use sourceUrl, sourceCommit, skillPath, sourceGone, and license. If the source is gone or its path is missing, stop. If license is null, read licence files at the source commit. > 3. Fetch only the source commit into a temporary Git repository. Do not clone full history. Derive repository_url from sourceUrl, including repository renames. If sourceCommit is absent, resolve the sourceUrl ref once. Set source_commit to that actual commit. Run these commands in one shell call: > > ```sh > git init --quiet "$temporary_dir" > git -C "$temporary_dir" fetch --quiet --depth=1 "$repository_url" "$source_commit" > git -C "$temporary_dir" checkout --quiet --detach FETCH_HEAD > ``` > > Read applicable licence declarations and notices at that commit. If copying is not permitted, report the restriction and stop. > 4. Inspect source entries together, then copy the directory containing skillPath into `./skills/replica-diff`. Use the user's path if selected. Keep the original SKILL.md, relative links, scripts, binary assets, and executable modes. Exclude .git metadata. Reject symlinks and paths outside the Skill directory. After checking entries, use cp -a where available. A regular source directory needs no custom copy script. Do not save this page wrapper as SKILL.md. > Preserve author credit, notices, and applicable licence files from repository or parent directories. Add PROVENANCE.md with the Skill page, source URL, actual commit, original path, and licence. Retain any existing PROVENANCE.md and record new provenance separately. Batch source inspection, copying, and provenance work where practical. > 5. In the project root, run `skilld install ./skills/replica-diff --mode copy --plain`. If skilld is unavailable, use `npx skilld install ./skills/replica-diff --mode copy --plain`. This known command needs no help lookup. Install does not support --json. Use detected Agent targets, or add --agent for the targets the user selected. Install the local path, never the upstream selector. If installation fails, preserve the local copy and report the exact failure. > 6. Confirm the local lockfile source and installed Agent copies once. Report the local path, actual commit, and Agent targets. After edits, reinstall the same local path. Upstream updates must not replace it. Do not publish or push unless the user asks. # replica-diff Two tools in this folder, both standard-library Python, no installs: ```bash python3 parity.py replica/features.csv # feature parity + missing list python3 imgdiff.py replica/screens/S07.png replica/clone-screens/S07.png --out diff-S07.png python3 imgdiff.py a.png b.png --json > replica/diffs/S07.json # for parity.py --visual python3 parity.py replica/features.csv --visual replica/diffs/*.json --markdown > replica/parity.md ``` ## What parity means here **Parity means it does the same job, not that it looks the same.** The feature score is the number that matters: can a user do everything they could do in the original. The layout score checks structure (is the information in the same places, in the same hierarchy), because that is what makes a switcher feel at home. It deliberately ignores colour, because replica-brand changes every colour on purpose. Do not chase pixel parity with the original. Its exact look is its trade dress, and it changes before launch. ## Step 1: feature parity Make sure `replica/features.csv` is current: every row's `clone` column is `yes`, `partial` (with a note), `no`, or `skip` (with a reason). Then: ```bash python3 parity.py replica/features.csv ``` It weights must 3, should 2, could 1, counts partial as half, leaves out `skip` rows and rows you added that the original does not have, and prints: the score, must-haves done of total, each area weakest first, and the missing list in build order. Must-haves not done means not shippable, and it says so. ## Step 2: layout diff For each key screen, take two screenshots at the **same viewport** (1440x900 desktop, 390x844 mobile) in the **same state** (same data shape, same tab open, logged in the same way). The original's come from public pages or the user's own account, saved in `replica/screens/`. The clone's go in `replica/clone-screens/`. ```bash python3 imgdiff.py replica/screens/S07.png replica/clone-screens/S07.png --out replica/diffs/S07.png ``` Layout mode (default) turns both into edge maps, cuts them into a grid, and compares where things are, scoring only cells with something in them. It reports the score (matches 90+, close 75+, partly 50+, different), the regions that differ (in the original's pixel coordinates, biggest first), and a height difference if the clone's page is much longer or shorter. Retina and non-retina screenshots compare fine: both are scaled to the same width. `--mode pixel` is exact comparison. Use it for your own regressions (clone today against clone last week), not against the original. ## Step 3: behaviour diff Walk each flow in both apps and compare what the scores cannot see: clicks to finish the core flow, what happens on errors, what is remembered between visits, what emails arrive. Fewer clicks than the original is a win. Write each difference as: flow, original does, clone does, fix or keep. ## Step 4: the report `replica/parity.md`: overall score, feature score, layout score per screen, missing features in build order, behaviour differences, and a verdict: - **not shippable**: any must-have missing, or any open S1 bug - **shippable**: all must-haves done, feature score 80+, no open S1 or S2 - **better than the original**: shippable, plus fixes from replica-entrepreneur. This is the goal. A straight copy has no reason to exist. Give honest numbers. A clone at 62% is at 62%. ## Output `replica/parity.md`, the diff images, and the top five things to build next. Then `/replica-build` for the gaps, or `/replica-entrepreneur` if parity is there.