Vivarium
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      • // CONTRACT v1 · OPEN SOURCE · APACHE-2.0

      Reproduce any bug.
      Any language.
      Any environment.

      Vivarium is a three-layer reproduction substrate. WebAssembly for milliseconds, Docker for fidelity, and a third layer for everything else. Problem first, technology second.

      Read the overviewView on GitHub
      vivarium.dev/layer1-wasm/cpython-137205
      WASM
      VIVARIUM · LAYER 1 · PYODIDE · SQLITE3

      Reproducing python/cpython#137205

      PRAGMA foreign_keys silently dropped under autocommit=False.

      ✕ UNREPRODUCED|fk_off ≠ fk_on
      # repro.pyimport sqlite3def test_fk():conn = sqlite3.connect(':memory:')fk_on = conn.execute('PRAGMA foreign_keys').fetchone()[0]assert fk_on == 1
      ElementsConsoleNetworkSources1 error
      ›await pyodide.runPythonAsync(repro)
      ✕AssertionError: 0 != 1
      at test_fk (repro.py:5)
      vivarium.dev/layer2-docker/postgres-lost-update
      DOCKER
      VIVARIUM · LAYER 2 · DOCKER · POSTGRESQL

      Reproducing PostgreSQL lost-update under READ COMMITTED

      Concurrent UPDATEs lose writes when a SELECT-then-UPDATE pattern omits row-level locks.

      RUNNING — tx-1 ⨯ tx-2
      # compose-up.shdocker compose up -dpsql -c "SET TRANSACTION ISOLATION LEVEL READ COMMITTED"parallel ./tx.sh ::= 1 2
      container.logtx-1.logtx-2.logrunning
      ›[docker] Pulling postgres:15-alpine
      ✓postgres ready in 74ms
      ›tx-1: UPDATE accounts SET balance = balance + 100
      ›tx-2: UPDATE accounts SET balance = balance - 50
      waiting for both transactions to commit…
      vivarium.dev/layer1-wasm/ruby-21709
      WASM
      VIVARIUM · LAYER 1 · RUBY.WASM · UNICODE

      Reproducing ruby/ruby#21709

      String#unicode_normalize edge case for combining diacritics in NFD form.

      ✓ REPRODUCED — bug reproduced
      # repro.rbs = "café"nfd = s.unicode_normalize(:nfd)back = nfd.unicode_normalize(:nfc)raise "round-trip lost" unless s == back
      ElementsConsoleNetworkSourcesverified
      ›await rubyVm.evalAsync(repro)
      ✓round-trip lost (RuntimeError raised as expected)
      verdict: REPRODUCED — issue#21709 reproducible in ruby.wasm

      // SHIPPED · 2026

      11
      reproductions catalogued
      4
      MCP tools
      6
      phases closed
      v1
      public contract

      // THREE-LAYER ARCHITECTURE

      Pick the layer that fits your bug.

      You never choose by hand — each recipe declares its own layer. The layers exist because no single runtime fits every bug.

      L1

      Browser-native, instant.

      WebAssembly runtimes inside the visitor’s tab. Algorithms, parsers, in-memory database operations. Startup in milliseconds to seconds.

      Pyodide · sqlite-wasm · wasm32-wasip1 · Ruby.wasm · PHP.wasm
      L2

      Container fidelity.

      Real filesystem, real processes, real network. Catalogue model: pinned Dockerfile + GHCR image. The visitor reproduces locally with one `docker run`.

      Docker · Firecracker · gVisor
      L3

      Record-replay & deterministic.

      Heisenbugs only. Vivarium pre-records the trace; the visitor replays. Burned-in GHCR images run on commodity Linux hosts — no PMU required.

      rr · Antithesis · CRIU · WASI Preview 3+

      // WHERE TO START

      Pick your starting point.

      Five minutes, five hours, or five months — the path is different.

      TRY ONE

      Open one reproduction in 5 minutes

      No install, no account. Click a recipe, watch the verdict resolve from pending.

      Open
      INTEGRATE

      Wire Vivarium into your repo

      Drop a `.vivarium/manifest.toml` and the reusable workflow checks your verdicts on every push.

      Open
      AI AGENT

      Drive Vivarium from Claude or Aider

      The `@aletheia-works/vivarium-mcp` server exposes four tools. List recipes, fetch verdicts, match an error string.

      Open
      CONTRIBUTE

      Write your first reproduction

      Scaffold a Layer 1 recipe directory and watch it appear in the gallery on the next deploy.

      Open

      // SEE IT RUN

      Eleven real upstream bugs, running in a browser tab.

      pandas, numpy, CPython, Ruby, PHP, Rust regex on Layer 1. PostgreSQL, bash, flock, find/xargs on Layer 2. coreutils sort race on Layer 3.

      Browse the gallery →Read the spec