# Sync a fork

> Bring a fork's branch up to date with its parent: branch (the fork's default branch when left out) takes in the parent's branch of the same name, or the parent's default branch for the fork's default branch.

<div class="g1t-endpoint"><span class="g1t-method" data-method="post">POST</span><code>/repos/{owner}/{name}/merge-upstream</code></div>

Needs the Write role on the fork and read access to its parent. A branch that is only behind moves forward (fast_forwarded); one with commits of its own gets a merge commit when the two sides' changes do not clash, edits to the same file merging line by line (merged); when both changed the same lines (or one deleted a file the other changed, or both changed a binary file) nothing is changed (conflicted, with the files in conflicts, at most 20): merge the parent's branch in a clone and push, or open a pull request. Returns status, branch, head (the branch's commit afterwards), behind and ahead (the commits each side had that the other lacked).

`status` is `up_to_date`, `fast_forwarded`, `merged` (a merge commit joins the fork's own commits and the parent's) or `conflicted`: both sides changed the files in `conflicts`, and nothing was changed. Merge the parent's branch in a clone and push. Refused with `422` when the repository is not a fork, `403` without the Write role on it, and `404` when its parent is gone or you can no longer read it. See [Sync a fork](/guides/forking-repositories/#sync-a-fork).

- **Authentication:** Required. Send an [access token](/reference/api/#authentication) as `Authorization: Bearer`.
- **MCP tool:** [`repository`](/reference/mcp/#repository) with `action` `sync_fork`, and the same inputs
- **Scope:** An access token needs [`repo:write`](/guides/authentication/#scopes).

## Path parameters

| Name | Type | Required | Description |
| --- | --- | --- | --- |
| `owner` | string | Yes | The workspace that owns the repository. |
| `name` | string | Yes | The repository's name. |

## Body parameters

Send a JSON object. Names are `snake_case`, as in responses; the `camelCase` spelling is accepted too.

| Name | Type | Required | Description |
| --- | --- | --- | --- |
| `branch` | string | No | The fork's branch to sync; its default branch when left out. |

## Example request

```sh
curl -X POST https://api.g1t.sh/repos/flagon-io/hello/merge-upstream \
  -H "Authorization: Bearer $G1T_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{
    "branch": "main"
  }'
```

## Example response

A successful request answers `200` with:

```json
{
  "status": "fast_forwarded",
  "branch": "main",
  "head": "9c4e1f0b7a2d3e5f6a8b9c0d1e2f3a4b5c6d7e8f",
  "behind": 3,
  "ahead": 0,
  "conflicts": []
}
```

## Errors

A failed request answers with one of these statuses and a body like `{"error": {"code": "not_found", "message": "Repository not found."}}`. See [errors](/reference/api/#errors).

| Status | Code | When |
| --- | --- | --- |
| 401 | `unauthenticated` | A token is required, or the one sent is not valid. |
| 403 | `forbidden` | The token is valid but not allowed to do this, such as a member-only change, or a token without the scope it needs. |
| 404 | `not_found` | It does not exist, or you cannot see it. |
| 409 | `conflict` | The request conflicts with the current state. |
| 422 | `invalid` | The input is not valid. `message` says which field and why. |