Start trigger

Start is the default entry point on a new workflow. It accepts editor input, API input, and deployed chat messages. Keep it when those callers should share the same downstream logic; add other triggers for events or schedules.

Input format

Open Start's Inputs and add fields. Each field has a name, type, description, and optional default value.

Setting	Behavior
Name	Downstream reference, such as `<start.customerId>`
Type	`string`, `number`, `boolean`, `object`, `array`, or a file field (`file[]` / `files`)
Description	Explains the input; also supplies the default MCP parameter description
Default value	Prefills editor runs and supplies a fallback when input is omitted or `null`
Order	Controls the editor form's field order

A supplied value overrides the default, including an empty string. Sim coerces supported primitive values; an invalid declared number or boolean can fail the run at input validation. Add an early Condition when your workflow needs stricter validation, such as a nonempty customer ID.

Per entry point

Click Run to fill the form created from Inputs. Defaults prefill it; submitting sends those values to <start.fieldName>. File fields accept uploads into their named output.

Put fields inside the API request's input value:

{
  "input": {
    "customerId": 4821,
    "message": "Please check my order"
  }
}

These values are available as <start.customerId> and <start.message>. File fields use uploaded-file metadata: upload the file first, then invoke the workflow. See API deployment.

Deployed chat supplies the latest message in <start.input>, the conversation ID in <start.conversationId>, and attachments in <start.files>. Custom fields use their declared defaults unless the execution surface supplies a matching value.

The public chat POST accepts input, conversationId, and files, plus its authentication fields; it is not a general structured-input launch API. Configure Agent Memory if later messages should use prior conversation context.

Outputs

These examples use a block named Start:

Reference	Value
`<start.fieldName>`	A named input field
`<start.input>`	Built-in input, including the latest message for Chat
`<start.conversationId>`	Supplied conversation ID, commonly from Chat
`<start.files>`	Supplied attachments normalized for the run

The built-in fields are not restricted to Chat; they are populated when the caller or configured input supplies them. Start also passes through supported additional runtime fields. Check the output panel rather than assuming a missing field is populated.

Run metadata

In advanced mode, enable Add run metadata to expose trusted server-built identity and run context under <start.metadata>: subject, workspaceId, workflowId, executionId, executionType, executionMode, and startTime.

The subject identifies the authenticated Sim user, chat email, or supported external identity without exposing credentials. When enabled, metadata is reserved; a caller cannot replace it with its own value. Execution-control field names are also reserved and rejected as Start outputs.

Multiple triggers

A workflow can have several trigger blocks. When the editor chooses among alternatives on the same path, Start takes priority, followed by Schedule and external triggers. Choose an external trigger explicitly when testing that entry point; its expected output shape can supply a mock payload.

The v2 manual API requires run.entry.blockId when several triggers are runnable. If you request a mock payload, do not also supply input. Each execution begins at its selected trigger; deployment is required for automatic events, while editor runs test the draft.