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# Headless mode

Mastra Code can run non-interactively — both from your shell and programmatically from Node or CI. Both paths share one core runner, `runMC`. The CLI is a thin adapter over it.

- **CLI**: `mastracode --prompt "..."` parses flags, bootstraps Mastra Code, runs the task, prints output, and exits with a status code.
- **Programmatic**: you bootstrap Mastra Code once with [`createMastraCode()`](https://code.mastra.ai/reference), then call `runMC()` to run a task as an async-iterable that also resolves to a typed result.

## CLI usage

Pass `--prompt` (or `-p`) to run a single task and exit:

```sh
mastracode --prompt "Fix the bug in auth.ts"
```

To open the interactive UI with a first message already sent, use `--tui-prompt` instead, or `--tui-initial-prompt` to send it only when there is no earlier conversation for the directory to resume.

Prompts can also be piped via stdin by passing `-` as the prompt:

```sh
echo "Summarize the repo" | mastracode --prompt -
```

### Flags

| Flag                         | Description                                                                                                                                                                                                                                                                                   |
| ---------------------------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| `--prompt`, `-p <text>`      | The task to execute (required, or pipe via stdin)                                                                                                                                                                                                                                             |
| `--continue`, `-c`           | Resume the most recent thread instead of creating a new one                                                                                                                                                                                                                                   |
| `--thread`, `-t <id>`        | Resume a specific thread by ID                                                                                                                                                                                                                                                                |
| `--title <title>`            | Set or rename the thread title                                                                                                                                                                                                                                                                |
| `--clone-thread`             | Clone the current thread before running (work on a copy)                                                                                                                                                                                                                                      |
| `--resource-id <id>`         | Set the resource ID for thread scoping                                                                                                                                                                                                                                                        |
| `--timeout <seconds>`        | Exit with code 2 if not complete within the timeout                                                                                                                                                                                                                                           |
| `--max-turns <n>`            | Abort after N agentic turns (exit code 1)                                                                                                                                                                                                                                                     |
| `--permission-mode <mode>`   | How tool approvals/suspensions resolve: `auto` (default) approves everything; `deny` refuses approvals and aborts on suspension                                                                                                                                                               |
| `--output`, `-o <mode>`      | Output mode: `human` (default), `json`, or `jsonl`                                                                                                                                                                                                                                            |
| `--model`, `-m <id>`         | Model override (e.g. a `provider/model` id). Takes precedence over the pack's model for the active mode                                                                                                                                                                                       |
| `--pack <id>`                | Start with a model pack: a built-in pack id (e.g. `anthropic`, `openai`), `custom:<name>`, or a bare custom-pack name. Applies the pack like `/models` → Activate (mode models, subagent models, model route) and makes it the default pack; also takes precedence over `MASTRACODE_MODEL_ID` |
| `--mode <build\|plan\|fast>` | Execution mode — defaults to `build` if omitted. `fast` selects Explore mode                                                                                                                                                                                                                  |
| `--thinking-level <level>`   | Thinking level: `off`, `low`, `medium`, `high`, `xhigh`, `max`                                                                                                                                                                                                                                |
| `--settings <path>`          | Path to a `settings.json` file (default: global settings)                                                                                                                                                                                                                                     |
| `--help`, `-h`               | Show usage                                                                                                                                                                                                                                                                                    |

`--continue` and `--thread` cannot be used together.

### Output modes

| Mode    | Behavior                                                                                                                              |
| ------- | ------------------------------------------------------------------------------------------------------------------------------------- |
| `human` | Streaming assistant text to stdout; tool activity and errors to stderr                                                                |
| `json`  | A single final JSON object (text, usage, tool calls/results, threadId, status)                                                        |
| `jsonl` | Newline-delimited JSON: one line per event except `display_state_changed` UI snapshots, then a final `{ "type": "result", ... }` line |

### Exit codes

| Code | Meaning                                            |
| ---- | -------------------------------------------------- |
| `0`  | Run completed successfully (`completed` or `done`) |
| `1`  | Error, aborted, or max turns reached               |
| `2`  | Timeout                                            |

### Examples

```sh
# JSON output with a timeout
mastracode --prompt "Add tests" --timeout 300 --output json

# Event stream
mastracode --prompt "Refactor" --output jsonl

# Gate a CI run: no unattended tool execution, bounded turns
mastracode --prompt "Review this PR" --permission-mode deny --max-turns 10

# Use a CI-specific settings file
mastracode --settings ./settings-ci.json --prompt "Run tests"

# Run on a custom model pack, with one mode's model overridden
mastracode --pack custom:Kimi --model anthropic/claude-opus-5-5 --prompt "Review this PR"

# Resume the most recent thread
mastracode -c --prompt "Continue where you left off"
```

## Programmatic usage

Bootstrap Mastra Code with [`createMastraCode()`](https://code.mastra.ai/reference), then pass the returned `controller` and `session` to `runMC()`. `createMastraCode()` is async; `runMC()` is synchronous and returns a run handle immediately. Pass `planApprovalStartsGoal: false` because `runMC()`'s default `autoApprovePolicy` approves submitted plans without starting a goal, so the agent shouldn't be told one will start.

```typescript title="src/run.ts"
import { createMastraCode, runMC } from 'mastracode'

const { controller, session } = await createMastraCode({ planApprovalStartsGoal: false })

const run = runMC({
  controller,
  session,
  prompt: 'Fix the failing test in auth.test.ts',
})

// Optional: stream live events as they happen.
for await (const event of run) {
  console.log(event.type)
}

// Resolves once the run completes, times out, errors, or is aborted.
const result = await run.result
console.log(result.status, result.text)
```

`runMC` never calls `process.exit` and never writes to global streams, so it is safe to embed in CI scripts and servers.

### The run handle

`runMC` returns an `MCRun`, which is both an async-iterable over controller events and a handle that resolves to a final result:

```typescript
const run = runMC({ controller, session, prompt })

run.result // Promise<RunMCResult>
run.abort() // abort the in-flight run
for await (const event of run) {
  /* ... */
}
```

Both `for await (const event of run)` and `await run.result` work on the same run. Awaiting `result` without iterating still drains events internally.

### `runMC` options

| Option          | Type                                                         | Description                                                                         |
| --------------- | ------------------------------------------------------------ | ----------------------------------------------------------------------------------- |
| `controller`    | `AgentController`                                            | Controller from `createMastraCode()` (required)                                     |
| `session`       | `Session`                                                    | Session from `createMastraCode()` (required)                                        |
| `prompt`        | `string`                                                     | The task to run (required unless `goal` is set)                                     |
| `goal`          | `RunMCGoalOptions`                                           | Run a goal instead of a prompt. Requires `objective`, `judgeModelId`, and `maxRuns` |
| `model`         | `string`                                                     | Explicit model id override; takes precedence over `mode`                            |
| `mode`          | `'build' \| 'plan' \| 'fast'`                                | Execution mode; resolves a model from `modeDefaults` when `model` is absent         |
| `modeDefaults`  | `Record<string, string>`                                     | Per-mode default model ids                                                          |
| `thinkingLevel` | `'off' \| 'low' \| 'medium' \| 'high' \| 'xhigh' \| 'max'`   | Thinking-effort level                                                               |
| `thread`        | `{ id?: string; continueLatest?: boolean; clone?: boolean }` | Thread selection / mutation                                                         |
| `resourceId`    | `string`                                                     | Resource id for thread scoping                                                      |
| `title`         | `string`                                                     | Set or rename the thread title before running                                       |
| `timeoutMs`     | `number`                                                     | Abort with `status: 'timeout'` (exit code 2) if not complete in time                |
| `maxTurns`      | `number`                                                     | Abort with `status: 'max_turns'` (exit code 1) after N assistant turns              |
| `policy`        | `ResolutionPolicy`                                           | How approvals/suspensions resolve (defaults to `autoApprovePolicy`)                 |
| `signal`        | `AbortSignal`                                                | External abort signal; aborting it aborts the run                                   |

### `RunMCResult`

| Field          | Type                                                                                    | Description                                                         |
| -------------- | --------------------------------------------------------------------------------------- | ------------------------------------------------------------------- |
| `status`       | `'completed' \| 'done' \| 'paused' \| 'error' \| 'aborted' \| 'timeout' \| 'max_turns'` | How the run ended. `done` and `paused` are terminal goal-run states |
| `text`         | `string`                                                                                | Aggregated assistant text across the run                            |
| `objective`    | `string`                                                                                | Goal objective for a goal run                                       |
| `goalEvent`    | `AgentControllerEvent`                                                                  | Terminal goal evaluation for a goal run                             |
| `reason`       | `string`                                                                                | Goal reason, when the goal evaluation provides one                  |
| `iterations`   | `number`                                                                                | Goal iterations completed                                           |
| `maxRuns`      | `number`                                                                                | Maximum goal runs configured for the goal                           |
| `finishReason` | `string`                                                                                | Underlying finish reason when the run finished normally             |
| `usage`        | `{ inputTokens?; outputTokens?; totalTokens? }`                                         | Token usage                                                         |
| `toolCalls`    | `Array<{ id; name; args }>`                                                             | Tool calls made during the run                                      |
| `toolResults`  | `Array<{ id; name; result; isError }>`                                                  | Tool results                                                        |
| `threadId`     | `string`                                                                                | The thread the run executed in                                      |
| `error`        | `{ name; message; stack? }`                                                             | Present when `status` is `error`                                    |
| `exitCode`     | `number`                                                                                | `0` success, `1` error/aborted/max\_turns, `2` timeout              |

## Resolution policies

A resolution policy decides how the run resumes `tool_approval_required` and `tool_suspended` events when there is no human in the loop. The default is `autoApprovePolicy`, which reproduces the historical headless behavior: approve every tool, auto-resolve sandbox and `submit_plan` suspensions, and answer any other suspension with a "use your best judgment" instruction.

Two built-in policies and a resolver are exported:

| Export                         | Behavior                                                               |
| ------------------------------ | ---------------------------------------------------------------------- |
| `autoApprovePolicy`            | Approve every tool; auto-resolve suspensions (default)                 |
| `denyPolicy`                   | Refuse every tool approval; abort on any suspension                    |
| `permissionModeToPolicy(mode)` | Resolve a `PermissionMode` (`'auto'` or `'deny'`) to a built-in policy |

The CLI `--permission-mode` flag maps directly onto these via `permissionModeToPolicy`.

### Custom policies

Implement the `ResolutionPolicy` interface to make per-event decisions. `onToolApproval` runs when a tool requests approval and returns `'approve'` or `'deny'`. `onSuspension` runs when a tool suspends and returns `{ resumeData }` to resume it or `{ abort: true }` to abort the run. A policy doesn't choose which tools the agent can use. For a read-only run, also select Explore mode with `mode: 'fast'`, whose tool set excludes writes and shell commands.

```typescript title="src/strict-policy.ts"
import { createMastraCode, runMC, type ResolutionPolicy } from 'mastracode'

const readOnlyPolicy: ResolutionPolicy = {
  // Only approve reading files with view; deny everything else.
  onToolApproval(event) {
    return event.toolName === 'view' ? 'approve' : 'deny'
  },
  // Abort rather than answer suspensions unattended.
  onSuspension() {
    return { abort: true }
  },
}

const { controller, session } = await createMastraCode({ planApprovalStartsGoal: false })

const run = runMC({
  controller,
  session,
  prompt: 'Audit the codebase for secrets',
  mode: 'fast',
  policy: readOnlyPolicy,
})

const result = await run.result
```

`onToolApproval` returns `'approve'` or `'deny'`. `onSuspension` returns either `{ resumeData }` to resume the suspended tool or `{ abort: true }` to abort the run.

## Next steps

- [Customization](https://code.mastra.ai/customization) — extend Mastra Code with custom modes, tools, and subagents.
- [API reference](https://code.mastra.ai/reference) — full `createMastraCode()` options and return values.