replica-diff

Two tools in this folder, both standard-library Python, no installs:

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:

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/.

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.