---
url: /reference/InputOptions.devtools.md
---
# devtools

* **Type**: object with the properties below
* **Optional**
* **Experimental**

Devtools integration options.

When enabled, Rolldown writes JSON-lines devtools output under
`node_modules/.rolldown/{session_id}/`, resolved against [`cwd`](./InputOptions.cwd).
Consumers can parse the output with `@rolldown/debug` after
`await bundle.close()` resolves.

`sessionId` replaces the generated session id. It must be one path segment: not empty, not
`.` or `..`, and without `/`, `\` or NUL. Rolldown does not check that it is unique: give each
bundler that runs at the same time its own `sessionId`, or their devtools output mixes.
The name `unknown-session` is reserved regardless of case.

## sessionId?

* **Type**: `string`
* **Optional**