@mastra/core/dist/docs/references/reference-workflows-run-methods-start.md

Mastra is a framework for building AI-powered applications and agents with a modern TypeScript stack.

# Run.start()

The `.start()` method starts a workflow run with input data, allowing you to execute the workflow from the beginning.

## Usage example

```typescript
const run = await workflow.createRun()

const result = await run.start({
  inputData: {
    value: 'initial data',
  },
})
```

## Parameters

**inputData** (`z.infer<TInput>`): Input data that matches the workflow's input schema

**requestContext** (`RequestContext`): Request Context data to use during workflow execution

**outputWriter** (`(chunk: TOutput) => Promise<void>`): Optional asynchronous function to handle output chunks as they are produced

**tracingContext** (`TracingContext`): Tracing context for creating child spans and adding metadata. Automatically injected when using Mastra's tracing system.

**tracingContext.currentSpan** (`Span`): Current span for creating child spans and adding metadata. Use this to create custom child spans or update span attributes during execution.

**tracingOptions** (`TracingOptions`): Options for Tracing configuration.

**tracingOptions.metadata** (`Record<string, any>`): Metadata to add to the root trace span. Useful for adding custom attributes like user IDs, session IDs, or feature flags.

**tracingOptions.requestContextKeys** (`string[]`): Additional RequestContext keys to extract as metadata for this trace. Supports dot notation for nested values (e.g., 'user.id').

**tracingOptions.traceId** (`string`): Trace ID to use for this execution (1-32 hexadecimal characters). If provided, this trace will be part of the specified trace.

**tracingOptions.parentSpanId** (`string`): Parent span ID to use for this execution (1-16 hexadecimal characters). If provided, the root span will be created as a child of this span.

**tracingOptions.tags** (`string[]`): Tags to apply to this trace. String labels for categorizing and filtering traces.

**outputOptions** (`OutputOptions`): Options for output configuration.

**outputOptions.includeState** (`boolean`): Whether to include the workflow run state in the result.

## Returns

**result** (`Promise<WorkflowResult<TState, TOutput, TSteps>>`): A promise that resolves to the workflow execution result containing step outputs and status

**traceId** (`string`): The trace ID associated with this execution when Tracing is enabled. Use this to correlate logs and debug execution flow.

**spanId** (`string`): The root span ID associated with this execution when Tracing is enabled. Use this for span-level lookup and correlation.

## Extended usage example

```typescript
import { RequestContext } from '@mastra/core/request-context'

const run = await workflow.createRun()

const requestContext = new RequestContext()
requestContext.set('variable', false)

const result = await run.start({
  inputData: {
    value: 'initial data',
  },
  requestContext,
})
```

## Related

- [Workflows overview](https://mastra.ai/docs/workflows/overview)
- [Workflow.createRun()](https://mastra.ai/reference/workflows/workflow-methods/create-run)