Environment variables keep configuration and secrets out of your code — define them once and read them at runtime. They come in two layers and two kinds.

Two layers: App base + per-entity override

Set a variable on an App and it's the shared base for everything in that app. A playground, workflow, stream, or agent can define a variable with the same key to override the app value just for itself; any key it doesn't redefine falls back to the app value. Each of those five surfaces has its own Environment variables editor.

Plain vs secure

A plain variable stores its value as-is and can be read wherever it's available (including a playground's browser code). A secure variable is encrypted at rest and is write-only: after you save it the UI shows it masked (••••••••) and re-reading never reveals it — to change a secret you submit a fresh value. Secure values are also scrubbed from run logs and artifacts.

Reading them in code

Server / runtime code — ctx.env

Playground server functions and stream binding functions receive a frozen ctx.env with both plain and secure values resolved:

exports.charge = async (ctx) => {
  const key = ctx.env.STRIPE_SECRET_KEY;   // secure value, decrypted at runtime
  const base = ctx.env.API_BASE_URL;       // plain value
  const res = await ctx.http.post(base + '/charges', { amount: 500 }, {
    headers: { Authorization: 'Bearer ' + key },
  });
  return res.data;
};

Playground browser code — flowfn.env

A playground's client-side JS can read plain variables via flowfn.env. Secure values are never sent to the browser, so they are absent here by design:

const base = flowfn.env.API_BASE_URL;   // plain only — secure keys are not present

Workflow placeholders — {{ env.KEY }}

In workflows, reference a variable anywhere a placeholder is allowed (task inputs, templates, code tasks) with {{ env.KEY }} (the {{ $env.KEY }} form also works). It resolves from the run's merged env; an unknown key is left untouched and a warning is logged, so a missing secret never becomes a silent empty value.

Authorization: Bearer {{ env.API_TOKEN }}

Agents resolve env for their tool calls, but there is no author-facing ctx.env inside an agent, and secure values are never placed in the prompt sent to the model.

Naming & limits

Keys match ^[A-Za-z_][A-Za-z0-9_]*$ — a letter or underscore first, then letters, digits, or underscores.
Reserved keys: NODE_ENV, PATH, HOME, PWD, USER, SHELL, and any key starting with FLOWFN_.
Up to 100 variables per owner; keys up to 128 characters; values up to 8 KB.