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Use the Chrome DevTools Protocol (CDP) method Page.captureScreenshot. It returns an image in the data field as a base64-encoded string. Send that method through an existing CDP connection—or through Chrome DevTools Protocol Monitor—not as a shell command. Decode the returned string and write the bytes to a PNG, JPEG, or WebP file.
This guide covers Protocol Monitor, raw WebSocket clients, viewport and full-page captures, clipping, encoding options, troubleshooting, and an API alternative.
What Page.captureScreenshot does
The Page domain’s Page.captureScreenshot method is described by Chrome as “Capture page screenshot.” A successful response has a data property containing base64-encoded image data. Your client decides how to decode and save those bytes.
The method accepts these documented controls:
| Option | Purpose | Important detail |
|---|---|---|
format |
Selects png, jpeg, or webp. |
PNG is the default. |
quality |
Controls lossy JPEG quality. | Integer from 0 through 100; it does not describe PNG quality. |
clip |
Captures a rectangle. | Uses x, y, width, height, and scale in a Page.Viewport object. |
captureBeyondViewport |
Requests content beyond the current viewport. | Documented default is false; the tip-of-tree reference marks it experimental. |
fromSurface |
Captures from the rendering surface rather than the view. | Documented default is true. |
optimizeForSpeed |
Requests faster image encoding. | Documented default is false; faster encoding can produce a larger file. |
Tip-of-tree protocol documentation can differ from the Chrome build you run. Check the protocol definition and behavior bundled with your target version, especially for experimental fields.
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Fastest route: DevTools Protocol Monitor
- Open the page in Chrome and open DevTools with More tools → Protocol monitor. If Protocol Monitor is not visible, open the DevTools command menu and search for it.
- Start a command entry and choose the
Pagedomain andcaptureScreenshotmethod. - Send parameters such as
{"format":"png"}, or send an empty object for defaults. - Inspect the response’s
datavalue. It is base64 text, so decode it before saving a file.
Protocol Monitor is useful for learning the exact JSON exchanged by DevTools. It also avoids writing a WebSocket client for a one-off capture.
Send the command over CDP
A CDP client first connects to a page target, enables the Page domain when required by its workflow, then sends a request with an incrementing numeric identifier. The request body is JSON:
{"id":1,"method":"Page.captureScreenshot","params":{"format":"png"}}The response associates the same id with a result:
{"id":1,"result":{"data":"iVBORw0KGgoAAA..."}}Decode only the result.data string. Do not save the base64 characters themselves as an image.
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Python example using a CDP WebSocket
This script uses the websocket-client package and Chrome’s local debugging endpoint. Start Chrome with remote debugging enabled, then replace the target URL and WebSocket URL with the values returned by Chrome’s debugging endpoint.
import base64
import json
import websocket
ws = websocket.create_connection("ws://127.0.0.1:9222/devtools/page/TARGET_ID", timeout=30)
next_id = 1
def call(method, params=None):
global next_id
request = {"id": next_id, "method": method}
if params is not None:
request["params"] = params
current_id = next_id
next_id += 1
ws.send(json.dumps(request))
while True:
message = json.loads(ws.recv())
if message.get("id") == current_id:
if "error" in message:
raise RuntimeError(message["error"])
return message["result"]
call("Page.enable")
result = call("Page.captureScreenshot", {"format": "png"})
with open("shot.png", "wb") as image:
image.write(base64.b64decode(result["data"]))
ws.close()Install the dependency with python -m pip install websocket-client. The script waits through unrelated CDP events until it receives the response matching its request id.
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Node.js example using the ws package
import WebSocket from 'ws';
import { writeFile } from 'node:fs/promises';
const ws = new WebSocket('ws://127.0.0.1:9222/devtools/page/TARGET_ID');
let id = 0;
const pending = new Map();
function call(method, params = {}) {
return new Promise((resolve, reject) => {
const requestId = ++id;
pending.set(requestId, { resolve, reject });
ws.send(JSON.stringify({ id: requestId, method, params }));
});
}
ws.on('message', async raw => {
const message = JSON.parse(raw.toString());
if (!message.id || !pending.has(message.id)) return;
const { resolve, reject } = pending.get(message.id);
pending.delete(message.id);
message.error ? reject(message.error) : resolve(message.result);
});
ws.on('open', async () => {
try {
await call('Page.enable');
const result = await call('Page.captureScreenshot', { format: 'png' });
await writeFile('shot.png', Buffer.from(result.data, 'base64'));
ws.close();
} catch (error) {
console.error(error);
ws.close();
process.exitCode = 1;
}
});Install the WebSocket client with npm install ws. Run the file as an ES module, and substitute the page target’s WebSocket URL.
Capture a region with clip
Pass a clip object when you need a rectangle rather than the whole viewport:
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"format": "png",
"clip": {
"x": 100,
"y": 200,
"width": 800,
"height": 500,
"scale": 1
}
}The coordinates and dimensions are device-independent pixels. A scale above 1 can increase output pixel density; verify the resulting dimensions in your image pipeline. Coordinates are relative to the page’s layout in the target viewport, so scrolling, zoom, emulation, and dynamic content can change what falls inside the rectangle.
Viewport, device emulation, and full-page captures
Set a viewport before capturing
For reproducible mobile or desktop output, configure metrics first with Emulation.setDeviceMetricsOverride, then capture:
{
"mobile": false,
"width": 1440,
"height": 900,
"deviceScaleFactor": 1
}The DevTools guide demonstrates this sequence, but it is an example rather than a universal device preset. Choose dimensions that match your test case and clear or replace the override when the session is complete.
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Request content beyond the viewport
Set captureBeyondViewport to true when you need a full-page-style image:
{"format":"png","captureBeyondViewport":true}The option’s documented default is false and it is experimental in the current tip-of-tree reference. Chromium behavior can use the actual page content size, so the resulting image may not equal the nominal viewport dimensions. Inspect the file’s width and height instead of assuming them.
Long pages can contain lazy-loaded images, sticky elements, animations, or content that changes while the capture is taken. For stable automation, wait for the page’s own ready condition, disable or freeze animations with page code when appropriate, and capture after layout has settled.
Choosing format and encoding
- PNG: lossless and the default; suitable for text, interfaces, and pixel comparisons.
- JPEG: useful when smaller lossy files are acceptable. Set
qualityfrom 0 to 100; this setting is documented for JPEG, not PNG. - WebP: supported by the protocol and often useful when your consumer accepts it.
- optimizeForSpeed: set to
truewhen encoding latency matters more than file size. The documented default isfalse.
There is no benchmark in the protocol definition that predicts your exact file size or capture time. Measure with your pages, viewport, format, and Chrome build.
Common failures and fixes
“Method not found” or an unknown parameter
Your Chrome build or target protocol may not support a tip-of-tree field. Remove experimental options first, then consult the protocol definition exposed by your target build. Keep the basic call—Page.captureScreenshot with format—as the compatibility baseline.
No image file or an unreadable file
Confirm that you decoded result.data from base64 and opened the output in binary mode. Saving the JSON response or base64 text directly will not create a valid image.
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Blank or incomplete output
Capture after navigation and layout have settled. Check that the target page is the intended CDP target, wait for required selectors or application state in your client, and account for lazy content and animations. For a full-page request, inspect output dimensions and test whether your Chrome version implements captureBeyondViewport as expected.
The clip is offset or the wrong size
Recheck device-independent-pixel coordinates, viewport metrics, page zoom, and scroll position. A clip is not a CSS selector; resolve an element’s bounding rectangle in page code and pass its numeric geometry.
Connection or target errors
Make sure Chrome was started with remote debugging, that the WebSocket URL belongs to a page target rather than a browser-level endpoint, and that the target remains open. Handle CDP events separately from responses and match each response by its numeric request id.
Or skip the browser setup
For a hosted capture, ScreenshotNeo provides a single GET request that returns PNG, JPEG, WebP, or PDF. It accepts cookie and consent banners as a visitor and removes more than 60 known consent platforms, newsletter popups, and chat widgets before capture; each cleanup step can be turned off. Bot checks or CAPTCHAs, blank pages, timeouts, failed loads, and cache hits cost nothing, and response headers report the page verdict and whether the request was billed. Its MCP server offers take_screenshot, get_page_info, and capture_pdf tools for Claude, Cursor, and other MCP clients.
Example cURL request (see the ScreenshotNeo documentation):
curl -G "https://api.screenshotneo.com/v1/shot" -d access_key=YOUR_API_KEY --data-urlencode url=https://stripe.com -o shot.webpPython
import requests
r = requests.get("https://api.screenshotneo.com/v1/shot", params={"access_key": "YOUR_API_KEY", "url": "https://stripe.com"}, timeout=90)
open("shot.webp", "wb").write(r.content)Node.js
const q = new URLSearchParams({ access_key: 'YOUR_API_KEY', url: 'https://stripe.com' });
const res = await fetch(`https://api.screenshotneo.com/v1/shot?${q}`);The Free plan includes 1,000 screenshots per month with no card. Paid plans start at $5 for 3,000 shots; every feature is on every plan. Create a free ScreenshotNeo account.
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When CDP is the better choice
- Use CDP when Chrome is already running in your test or automation process and you need precise control over targets, emulation, clipping, and protocol events.
- Use a hosted API when you do not want to manage Chrome processes, WebSocket targets, page readiness, consent cleanup, or retry logic.
- For either workflow, record the Chrome or service configuration, viewport, format, and capture parameters so later images can be compared fairly.
Frequently Asked Questions
Is Page.captureScreenshot a command-line command?
No. It is a CDP protocol method sent as JSON over a CDP connection or through DevTools Protocol Monitor.
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The result contains a base64-encoded image string in the data field; decode it to obtain file bytes.
Can CDP save a screenshot directly to a filename?
The protocol returns encoded data. Your client must decode and write the bytes to a file.
Does captureBeyondViewport always produce the same full-page dimensions?
No. The option is experimental in the tip-of-tree reference, and implementations can size the image from actual page content. Inspect the resulting dimensions.
Quick Recap
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