> ## Documentation Index
> Fetch the complete documentation index at: https://phaseo.app/docs/llms.txt
> Use this file to discover all available pages before exploring further.

# Apply Patch

> Let Responses models return validated patch operations.

Use `phaseo:apply_patch` when a Responses workflow should return file changes as structured patch operations. Phaseo validates the operation and returns it to your client; it does not mutate your filesystem or repository.

<Note>
  `phaseo:apply_patch` is available on `/v1/responses`.
</Note>

## Request

```bash theme={null}
curl https://api.phaseo.app/v1/responses \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "openai/gpt-5-nano",
    "input": "Create a small README patch for this project.",
    "tools": [
      { "type": "phaseo:apply_patch" }
    ]
  }'
```

## Operation Shape

When the model calls the tool, it sends an operation object:

```json theme={null}
{
  "operation": {
    "type": "update_file",
    "path": "/README.md",
    "diff": "@@ ...\n-Old text\n+New text\n"
  }
}
```

Supported operation types:

| Type          | Required fields |
| ------------- | --------------- |
| `create_file` | `path`, `diff`  |
| `update_file` | `path`, `diff`  |
| `delete_file` | `path`          |

## Tool Result

Phaseo returns the validated operation to the model loop:

```json theme={null}
{
  "status": "completed",
  "operation": {
    "type": "update_file",
    "path": "/README.md",
    "diff": "@@ ...\n-Old text\n+New text\n"
  },
  "message": "Patch operation validated. The client must apply or reject this patch and report the result."
}
```

Your application remains responsible for applying the patch, showing it to a user, rejecting it, or asking the model for a revised operation.

## Usage And Pricing

Phaseo records:

```json theme={null}
{
  "usage": {
    "server_tool_use": {
      "apply_patch_requests": 1
    }
  }
}
```

Pricing cards can bill this with the `server_tool_apply_patch_requests` meter.

## Related

* [Server Tools](./index)
* [Responses API](../../api-reference/endpoint/responses)