FINANCIAL-CORRECTNESS CRASH TESTING

Break your stock app
before the market does.

JustFair crash-tests stock applications against stock-market events before your users find the bugs. Scenarios, replay, root cause, fix guidance.

How It Works

HOW IT WORKS

Five steps to a crash-tested app.

Connect

Add two small adapter endpoints exposing what your app displays.

Test

Run JustFair scenarios locally against your running app.

Break

See exactly which financial invariant failed, with evidence.

Fix

Inspect the replay, root cause and remediation guidance.

Verify

Run the same scenario again until it passes.

COVERAGE

What JustFair tests.

Scenario packs target the places stock apps go financially wrong. Shown are direction examples; implemented scenarios are listed in each pack.

MARKET DATA

Stale and carried-forward prices. Implemented: carried-forward equity references must never read as live.

CORPORATE ACTIONS

Splits, lifecycle changes, expiries. Implemented: PreStocks conversion deadlines and expired holdings.

TOKEN BEHAVIOR

Token-2022 transfer-fee accounting. Implemented: gross-vs-net receipt on live T-Token fee state.

MARKET STRUCTURE

Meteora DBC liquidity and price-impact stress. Implemented: opening size against issuer-declared policy.

AGENT SAFETY

Financial state misread by autonomous agents. Directional pack; scenarios land as adapters mature.

REAL FAILURE

A swap succeeds. The money is still wrong.

TESSERA_TRANSFER_FEE_ACCOUNTING Engine-generated sample result

EXPECTED RECIPIENT 998 fee-adjusted T-OpenAI units

APP REPORTED 1000 gross transfer amount

RESULT FAIL Token-2022 transfer fee ignored

BUILT FOR DEVELOPERS

Expose two test endpoints. Run JustFair locally.

ADAPTER GET /justfair/v1/manifest and POST /justfair/v1/evaluate on your localhost app.

RUNNER npx justfair@latest test --target http://localhost:3100 --open

REPORT Open the result artifact in Replay Lab. Fix. Rerun.

Developer API

Deterministic scenario endpoints.

Run crash-test scenarios locally or query live DBC stress math from your own tooling.

GET /api/v1/health

curl -X POST https://justfair-theta.vercel.app/api/v1/dbc/whale \
  -H "Content-Type: application/json" \
  -d '{
    "configAddress": "DLa32CJBWDp3YveqD3A8jexkUUzeTZPjEquf3Ur6BwEU",
    "tradeSizeQuoteUnits": "1000000000",
    "maxPriceImpactPct": 8
  }'

Break it here before the market does it for you.

Run your first scenario locally. No account, no funds, no custody.

STEP 1 OF 4

Choose a Company

Select an underlying stock or ETF to inspect verified Solana tokenized representations across issuers.

JUSTFAIR · DEVELOPER ONBOARDING

Crash-test your stock app before users find the bugs.

Your proprietary code stays local. JustFair evaluates financial correctness against adverse market scenarios and real market infrastructure, with zero custody and zero telemetry.

STEP 1

Set up JustFair in your project

Open a terminal in the root folder of the stock app you want to test, then initialize configuration and a clean protocol adapter scaffold in that project without cloning JustFair. No repo clone required, no account required, no funds, and no private keys.

npx justfair@latest init

Creates justfair.config.js and justfair-adapter.mjs inside that project folder. Existing files are never overwritten.

STEP 2

Connect your app (The Observation Bridge)

JustFair needs a small observation adapter that reads values your real application calculates or displays.

Open justfair-adapter.mjs and point each observations assignment inside the POST /justfair/v1/evaluate handler at the value your app actually calculates or displays.

YOUR STOCK APP → OBSERVATION ADAPTER → JUSTFAIR → PASS / FAIL / UNABLE

if (scenarioId === "STALE_CARRIED_FORWARD_EQUITY") {
  // Replace with the price your app displays
  observations.displayedPrice =
    inputs?.referencePrice ?? 329.29;

  // Replace with whether your app claims it is live
  observations.claimsLive = true;
}

The adapter is the bridge: It translates your internal data into raw observations.
The adapter is NOT the product being tested: Your real application supplies the values.
Two separate ports: Your app can run on any localhost port. The adapter reads from it and exposes JustFair's two test endpoints on its own localhost port.
Observations only: Your app supplies what it displays; JustFair owns the financial judgment.

STEP 3

Start your app & adapter

Run your application (e.g. on port 4000) and start the observation adapter on localhost (e.g. port 3100).

node justfair-adapter.mjs

Adapter exposes GET /justfair/v1/manifest and POST /justfair/v1/evaluate on localhost (e.g. http://localhost:3100).

STEP 4

Run the financial crash test

Execute scenarios against your running adapter. Compatible scenarios run, incompatible scenarios skip honestly, invariants are evaluated with zero funds and zero signing. JustFair prints the quick PASS / FAIL / UNABLE result in your terminal, saves the detailed report locally as justfair-result.json, and with --open automatically opens that same report in Replay Lab.

npx justfair@latest test --target http://localhost:3100 --open

Tests stale/carry-forward equity prices, PreStocks conversion expiries, Meteora DBC price impact, and Tessera Token-2022 transfer fees.

STEP 5

Fix → Rerun → Pass

When an invariant fails, see the exact breakdown: FAIL → WHAT HAPPENED → EXPECTED VS YOUR APP → ROOT CAUSE → FIX GUIDANCE → REPLAY. Fix your app and rerun the exact same command, then watch it turn green.

Upload your justfair-result.json artifact manually or explore interactive sample failures.

View adapter specification & protocol contract

GET /justfair/v1/manifest returns {"adapterVersion": "1", "name": "...", "capabilities": [...]}.

POST /justfair/v1/evaluate receives {"scenarioId", "scenarioVersion", "inputs"} and returns only observations — never a verdict. JustFair owns PASS / FAIL.

Localhost targets only. Responses capped at 64 KB. Safe for confidential protocols and air-gapped test environments.

Break your stock app
before the market does.

Five steps to a crash-tested app.

Connect

Test

Break

Fix

Verify

What JustFair tests.

MARKET DATA

CORPORATE ACTIONS

TOKEN BEHAVIOR

MARKET STRUCTURE

AGENT SAFETY

A swap succeeds. The money is still wrong.

Expose two test endpoints. Run JustFair locally.

Deterministic scenario endpoints.

Break it here before the market does it for you.

Choose a Company

No supported stocks match your search.

Apple

What matters to you?

Loading Product Matches...

Key Representation Differences

What happens if...?

Verified Dividend Fact

Check the Trade

No representations match your search.

Crash-test your stock app before users find the bugs.

Set up JustFair in your project

Connect your app (The Observation Bridge)

Start your app & adapter

Run the financial crash test

Fix → Rerun → Pass

Understand a result.

Have a JustFair result?

Run report

Break your launch configuration before traders do.

Break your stock appbefore the market does.

Five steps to a crash-tested app.

Connect

Test

Break

Fix

Verify

What JustFair tests.

MARKET DATA

CORPORATE ACTIONS

TOKEN BEHAVIOR

MARKET STRUCTURE

AGENT SAFETY

A swap succeeds. The money is still wrong.

Expose two test endpoints. Run JustFair locally.

Not mocked integrations.

PRESTOCKS

METEORA DBC

TESSERA

Deterministic scenario endpoints.

Break it here before the market does it for you.

Choose a Company

No supported stocks match your search.

Apple

What matters to you?

Loading Product Matches...

Key Representation Differences

What happens if...?

Verified Dividend Fact

Check the Trade

No representations match your search.

Crash-test your stock app before users find the bugs.

Set up JustFair in your project

Connect your app (The Observation Bridge)

Start your app & adapter

Run the financial crash test

Fix → Rerun → Pass

Understand a result.

Have a JustFair result?

Run report

Break your launch configuration before traders do.

Break your stock app
before the market does.