file-format.md

File format

A file has a header and a body.

import { RECEIPT } from 'crw:lib/schemas'      // header: zero or more static imports ...
import { greeting } from './hello-lib.js'
export const meta = { name: 'hello', phases: ['greet'] }   // ... then exactly one meta
phase('greet')                                  // body: everything after the meta statement
const hi = await agent(greeting('crw'))         // top-level await
return { hi }                                   // top-level return: the run's result

• The header is zero or more static import statements followed by exactly one export const meta = <object literal>. An import has one of the forms import 'm', import d from 'm', import {a, b as c} from 'm', import * as ns from 'm' and import d, {a} from 'm'.
• meta must evaluate to a JSON-serialisable object. It is evaluated as an expression in a fresh runtime with no host globals, so it cannot call agent or read args, and under the same determinism stubs as the body (below), so Date.now(), Math.random(), new Date() and Date() in a meta are load errors. It is recorded in the run record.
• The body may use top-level await and top-level return. These are a CRW extension and the script is not standard ESM: the body runs as the body of an async function, and the value it returns is the run's result. A script in the shape Claude Workflow accepts (a meta and a body with top-level await and return, no imports) is a subset of this format.
• An import or export after the header, a dynamic import(), import.meta, and any export other than meta are load errors. The body is checked with a lexer that tracks strings, template literals (including their substitutions), comments and regular expression literals, so the words inside them are not taken for statements. A property call (o.import(x), also with whitespace or a comment between the dot and the name) and a method named import or export ({ import(x) { ... } }) are not imports; a method declaration is told from a call by the { that follows its parameter list on the same line.
• Script errors keep the body's line numbers: the header is replaced by blank lines in the executed text and the transform's source map is given to the runtime.