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

# Eval

> Evaluate a JavaScript expression in the browser

## Description

Executes a JavaScript expression in the context of the current page and returns the result.

## Authentication

Open-source deployments do not require authentication by default. If your server config enables `X-API-Key`, include that header with the request.

## Path Parameters

<ParamField path="id" type="string" required>
  The browser ID returned from Create Session.
</ParamField>

## Request Body

<ParamField body="expression" type="string" required>
  The JavaScript expression to evaluate.
</ParamField>

## Response

<ResponseField name="success" type="boolean">
  Whether the evaluation completed successfully.
</ResponseField>

<ResponseField name="data" type="object">
  The return value of the evaluated expression.
</ResponseField>

## Example

```bash theme={null}
curl -X POST http://localhost:8080/browsers/exc-b9534e98-c3ce-4d1b-9671-b563ac66adc3/eval/ \
  -H "Content-Type: application/json" \
  -d '{ "expression": "document.title" }'
```