Settings

Both SDKs read the same env vars. A value you pass in code (new Flow({ ... }) or flow.ClientOpts{...}) wins over the env var. An empty env var counts as not set.

Env var	Code (TS / Go)	Default	When it is not set
FLOW_SIGNING_KEY	signingKey / SigningKey	none	The endpoint answers every request with 500 NoSigningKey (unless dev mode). The sync at boot does nothing. Realtime calls get 401 from the engine.
FLOW_SIGNING_KEY_FALLBACK	signingKeyFallback / SigningKeyFallback	none	Only the main key is used.
FLOW_EVENT_KEY	eventKey / EventKey	none	Sending fails at once: flow.send needs an event key (eventKey or FLOW_EVENT_KEY) / flow: no event key (set FLOW_EVENT_KEY or ClientOpts.EventKey). Serving works.
FLOW_BASE_URL	baseUrl / BaseURL	https://worker.clevixstudio.com in v0.6.5; https://worker.flow.clevixstudio.com from the next release	The default is used.
FLOW_LOCAL_DEV	isDev / Dev	on when FLOW_BASE_URL is local, else off	1 turns dev mode on.

What each one does

FLOW_SIGNING_KEY is the app's own signing key, signkey- and 64 hex characters, from Add app in the dashboard. It is used to:

• check that each call to your endpoint (POST, GET) comes from the engine;
• sign the endpoint's answers;
• prove who the app is when it syncs, loads a big run's state, and publishes realtime messages.

A key that is not in the right form: TypeScript answers 500 NoSigningKey with the signing key is not in the format signkey-<64 hex chars>; Go's NewClient gives an error.

FLOW_SIGNING_KEY_FALLBACK is the old key while you rotate. Calls signed with either key are taken. When the engine answers 401 to the main key (on sync or realtime), the SDK tries the fallback.

FLOW_EVENT_KEY lets flow.send / client.Send send events. Only needed if the app sends events. step.sendEvent inside a function does not need it.

FLOW_BASE_URL is the engine's address. Set it only for a local engine (http://127.0.0.1:8787) or your own engine. The SDK uses it for sending events, sync, realtime, and loading a run's state when it is over 4 MB.

Dev mode turns off the signature check: the endpoint takes unsigned calls. It is on by itself when FLOW_BASE_URL is on localhost, 127.0.0.1 or host.docker.internal, and FLOW_LOCAL_DEV=1 turns it on for any address. isDev / Dev in code win over both: false keeps it off. For local work only. Never on a public app: anyone could start your functions. With a local engine, it also lets the app run with no FLOW_SIGNING_KEY and no FLOW_EVENT_KEY: the local engine takes its sync, events and calls with no key.

Where the SDK looks

• Node and Go: the process environment.
• Cloudflare Workers: the handler's env first (wrangler secrets and vars), then process.env. serve gets env by itself. For flow.send and flow.realtime, pass it: flow.send(event, { env }).

On Workers:

wrangler secret put FLOW_SIGNING_KEY
wrangler secret put FLOW_EVENT_KEY

For your own engine, put its URL in vars in wrangler.jsonc: "vars": { "FLOW_BASE_URL": "https://flow.example.com" }.

Options that are not env vars

TypeScript	Go	Default
serve({ syncOnBoot })	ClientOpts.NoSyncOnBoot	sync at boot on
serve({ streaming })	ClientOpts.NoStreaming, HeartbeatInterval	streamed answers on, heartbeat 20 s
new Flow({ fetch })	ClientOpts.HTTPClient	the global fetch / http.DefaultClient