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When to use render_js

Set "render_js": true when the content you need is injected by JavaScript after the initial HTML loads. Common cases:
  • Single-page applications (React, Vue, Angular)
  • Infinite-scroll feeds where items appear after JS executes
  • Pages behind login redirects that trigger on load
  • Dynamic price or inventory widgets
If the page’s HTML already contains the content (SSR pages, Wikipedia, static sites), skip render_js — it saves credits and latency.

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How it works

When render_js is true, the API launches a headless Chromium browser, navigates to the URL, waits for the network to settle, and captures the fully-rendered DOM. The browser is isolated per request and discarded afterwards. Rendering typically adds 2–5 seconds of latency.

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Waiting for specific conditions

Use wait_for to hold rendering until a specific condition is met: 
{
  "url": "https://example.com/dashboard",
  "render_js": true,
  "wait_for": { "network_idle": true },
  "output": ["html"]
}
network_idle: true waits until there are no in-flight network requests for 500 ms. This is useful for pages that fire background API calls after initial load.

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Setting a timeout

Use timeout_ms to cap how long the browser waits. The default is 15,000 ms (15 s) for inline requests. Async requests allow up to 300,000 ms (5 min). 
{
  "url": "https://example.com/slow-app",
  "render_js": true,
  "timeout_ms": 30000,
  "output": ["markdown"]
}
If the timeout is exceeded, the API returns a timeout error code.

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Device emulation

Emulate mobile or tablet viewports to reach responsive content: 
{
  "url": "https://m.example.com",
  "render_js": true,
  "device": "mobile",
  "output": ["html"]
}
Supported values: "desktop" (default), "mobile", "tablet".

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Sessions

Reuse a browser session across multiple fetches — cookies, local storage, and auth state are preserved: 
{
  "url": "https://app.example.com/page-2",
  "render_js": true,
  "session": { "id": "sess_abc123" },
  "output": ["markdown"]
}
See Identity & Sessions for the full session lifecycle.

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Cost

JS-rendered fetches cost 2 credits vs 1 for static fetches.