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

# Diff Viewer

# Diff Viewer

Fased ships a built-in `diff_view` tool. It creates a compact HTML diff artifact
under the Canvas host root and returns:

* added/removed line counts;
* the local artifact path;
* a Canvas URL such as `/__fased__/canvas/diffs/...html`.

This is a built-in Fased review tool, not a patch-application or
approval-bypass surface.

## Inputs

The tool accepts either:

* `before` and `after` text; or
* `unifiedDiff`.

Example prompt:

```text theme={"theme":{"light":"min-light","dark":"min-dark"}}
Use diff_view to compare this old text and new text, then give me the canvas URL.
```

## Where It Belongs

`diff_view` is a core Agent tool:

* enable/disable it in **Agent > Tools**;
* use it from chat, tasks, or channels when the Agent needs to present a change;
* use normal file tools or git commands to create the diff input.

The viewer is for review and presentation. It does not apply patches and it does
not bypass approval policy.

## Related

* [Apply Patch](/tools/apply-patch)
* [Browser and Canvas](/tools/browser)
* [Tools](/tools/index)