Performance & Sandbox

Measure FCP/LCP/CLS against a URL — or render HTML in an isolated sandbox, including a screenshot.

What you can do with performance and sandbox

Measure Core Web Vitals and timing metrics against a live URL — or render isolated HTML in a sandbox (with optional screenshot) without an external page.

FCP, LCP, CLS, TTFB, and resource counts
Console/page errors alongside metrics
Sandbox: HTML + optional resources, block_external
Sandbox screenshot for visual verification

API Call

editable

Request bodyJSON

{'{'}

{'}'}

Performance: settle_ms and viewport. Sandbox: toggle screenshot and block_external.

—

FCP ms

—

LCP ms

—

CLS

Run performance or sandbox to see metrics and output.

Endpoints & parameters

Pick an endpoint for a sample request and a clear list of parameters.

POST /v1/performance

Performance metrics for a public URL.

Example request

{
  "url": "https://example.com",
  "width": 1280,
  "height": 720,
  "settle_ms": 500
}

Parameters

Name	Type	Description
`url`req	string	Target URL.
`width / height`	number	Viewport for measurement.
`settle_ms / goto_timeout_ms`	number	Settle and navigation timeouts.