# twitter-archive/diffy

Find potential bugs in your services with Diffy

Repository: https://github.com/twitter-archive/diffy
Canonical: https://ross.abutalabs.com/products/diffy
Homepage: https://twitter.com/diffyproject
Language: Scala
License: Apache-2.0
License Family: permissive
Archived: true
Last push: 2020-07-01T19:13:06+00:00

## Health v2 (maintenance only)
Score: 10/100 (v2, computed 2026-09-03T02:20:16.233290+00:00)
- activity 0, release rhythm 35, longevity 100
- inputs: {"age_days": 4039, "days_push": 2254, "days_rel": null, "gap_med": null, "n_releases_24m": 0}
- flags: no_releases, archived
- formula: round(0.45*activity + 0.35*rhythm + 0.20*longevity); archived -> min(score, 10)

## Adoption (not part of the score)
Stars 3811, forks 360 (observed 2026-08-28T04:08:20.705705+00:00)

## What it is
Diffy is a proxy-based differential testing tool from Twitter that multicasts incoming requests to a candidate service and two known-good service instances, then compares responses to surface regressions. It filters out non-deterministic noise by measuring differences between two identical known-good instances.

## Use cases
- find regressions in a new version of my service without writing tests
- compare responses between old and new service implementations side by side
- detect bugs in my API by diffing candidate and known-good instances
- filter out noisy non-deterministic fields when comparing service responses
- run automated differential testing against microservices
- validate a rewritten service behaves equivalently to the original

## When to avoid
- the original repo is archived and unmaintained - use the community fork Opendiffy instead
- you need to test stateful services where side effects make response comparison unreliable
- you don't have the ability to run multiple instances of your service simultaneously

## Facets
- artifact type: service
- maturity: abandoned
- function: testing, proxy, middleware, http-server
- domain: testing, developer-tools, apis, backend
- platform: jvm, self-hosted
- tags: differential-testing, regression-detection, service-comparison, scala, twitter-archive, mirror-testing, docker

## Member repositories
- twitter-archive/diffy (main) score 10

## Provenance
- Observed fields: from GitHub, fetched 2026-08-28T04:08:20.705705+00:00.
- Health v2: computed from the inputs above; adoption is never an input.
- Inferred fields (summary, facets, guidance): AI-extracted, prompt v1, taxonomy v1, on 2026-08-29T18:26:37.500270+00:00, confidence not recorded.
  - readme: https://github.com/twitter-archive/diffy (fetched 2026-08-28T04:08:20.705705+00:00, sha 6135fc58e1cb)
- Data as of 2026-08-30T08:39:29.467469+00:00.