JSONata expressions

FetchCatch evaluates JSONata expressions in condition, transform, wait_for_event, HTTP input mappings, and decision responseValues.

Library: JSONata via Jsonata.Net.Native.

Run state available to expressions

Typical bindings (exact shape depends on flow):

After an http node runs:

nodes.http_fetch_user.status
nodes.http_fetch_user.body.fieldName

Common patterns

Condition

"expression": "nodes.http_fetch_user.body.balance >= input.amount"

HTTP input mapping

"inputs": {
  "userId": "input.userId",
  "filter": "\"active\""
}

Transform

"expression": "{ \"fullName\": nodes.http_1.body.firstName & ' ' & nodes.http_1.body.lastName }"

Decision with dynamic value

Prefix with = to evaluate as JSONata:

"responseValues": {
  "approved": true,
  "reason": "=nodes.cond_1.expression ? 'auto-approved' : 'manual review'"
}

Tips for AI agents

1. Quote strings inside JSONata correctly; the expression is a JSON string value.
2. Prefer input.field over deep paths when the start node declares inputSchema.
3. Reference HTTP bodies via nodes.{id}.body, not the raw response object.
4. Test complex expressions in the web console designer (Monaco + intellisense) before syncing.
5. Keep expressions pure — no side effects; runtime does not allow custom functions beyond JSONata standard.

Intellisense

The console exposes TypeScript declarations for input and prior node outputs. After pulling flows, use the designer for expression authoring when possible.

Public API: GET /v1/intellisense/... (console-authenticated) generates .d.ts from the graph.