Environments

JET environments differ in one important way: how much of the rail is backed by a real provider. Rather than making you guess, the API publishes it.

curl "$JET_API/capabilities"

{
  "version": "1.4.2",
  "environment": "sandbox",
  "corridors": [
    { "from": "USDC", "to": "VND", "destinationCountry": "VN", "ownedRail": false, "instant": false },
    { "from": "USDC", "to": "NGN", "destinationCountry": "NG", "ownedRail": false, "instant": false }
  ],
  "features": [
    { "feature": "transactions", "status": "live",    "reason": "…" },
    { "feature": "wallets",      "status": "partial", "reason": "…", "requires": "…" },
    { "feature": "banking",      "status": "planned", "reason": "…", "requires": "…" }
  ]
}

The environment field

Value	What it means
simulated	The full state machine runs, but external providers are simulators. Nothing settles in the real world. Use it to build and test your integration.
sandbox	Real provider sandboxes are wired. Value moves in test networks, not production money.
production	Live money.

Simulators are honest fakes: they implement the same interfaces as real providers and refuse to run in production. They never invent a success that a real provider would not have produced.

The features array

Each feature carries a status, so your client can adapt instead of discovering gaps by hitting them.

Status	What it means for you
live	Real endpoint, works now. Build on it.
partial	The reads work; the money-moving half is not wired yet. Expect 501 on the write.
simulated	Works end to end, against a simulator.
planned	No endpoint yet. Calling it returns 501.

When a feature is not available, the endpoint says so explicitly:

{
  "error": "not_implemented",
  "feature": "banking",
  "message": "wire transfers need a custody bank adapter",
  "requires": "a production banking partner"
}

Success

This is a promise, not an accident. An unwired feature returns 501 with a reason: never an empty list, never a fabricated success. An empty list because nothing is configured and an empty list because you genuinely have nothing must not look the same, so they don't.

Building against capabilities

The recommended pattern is to fetch /capabilities at startup, cache it, and gate your UI and your retry logic on it:

const caps = await fetch(`${base}/capabilities`).then(r => r.json());

const canSendTo = (country: string) =>
  caps.corridors.some((c) => c.destinationCountry === country);

Do not hard-code the corridor list. It grows, and /capabilities is the only place that is guaranteed to be current for your environment.

Health

GET /health is the liveness check, separate from capabilities:

{ "status": "ok", "version": "1.4.2", "uptimeSeconds": 41822, "checks": { "temporal": "ok" } }

It returns 503 with "status": "degraded" when the workflow engine is unreachable. In that state the API cannot start new payments: every payment is a durable workflow, so there is no degraded mode where sends quietly proceed without one. Reads generally still work.

Point your load balancer and your uptime monitor at /health; point your feature flags at /capabilities.

Sandbox tools

A sandbox talks to the providers' own test environments, where nobody sends a real bank transfer and some account numbers are magic. Three endpoints exist only there, to drive a flow end to end. Each answers 501 on any other environment. They are listed under Sandbox tools in the API reference.

Endpoint	What it does
GET /treasury/sandbox-prefill	Per corridor, a beneficiary and an amount the sandbox providers are proven to settle, plus off-ramp beneficiaries and each provider's sandbox outcome rules. Use it to fill a form rather than guessing values
POST /treasury/onramps/simulate-wire	Makes a wire arrive at our account quoting your reference, for the amount you name. It is matched and converted exactly as a real wire is
POST /treasury/onramp/:onRampId/simulate-payment	For a deposit the payer pays on a provider's page: marks that payment as made at the provider

Each one fakes only the outside party, never JET's side: what happens after the simulated payment is the same code that handles real money.

Warning

Sandbox values are not real. An account number that settles in a sandbox is somebody else's account, or nobody's, in production.