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Use Chrome DevTools Protocol’s Page.captureScreenshot method. It returns a base64-encoded image, so your client must decode the data field and write the bytes to a file. You can send the method through DevTools Protocol Monitor or through a CDP WebSocket connection opened by your automation code.
This guide shows both workflows, explains every capture option, and covers viewport, clipped-region, device-emulation, and full-page captures. The protocol reference is tip-of-tree, so check the definition and behavior shipped with the Chrome build you target before relying on experimental fields.
What you need before sending a screenshot command
- A running Chrome or Chromium instance with remote debugging enabled, or Chrome DevTools opened on the page you want to inspect.
- A CDP client connection to the target page. CDP methods are protocol messages, not shell commands.
- A way to decode base64 and save binary output when you are not using Protocol Monitor.
For a locally launched browser, a typical debugging start command is:
google-chrome --remote-debugging-port=9222Use the executable and profile arrangement appropriate for your operating system. Exposing a debugging port can grant control over browser tabs, cookies, and logged-in sessions; bind it to localhost and do not expose it to an untrusted network.
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Option 1: Capture with DevTools Protocol Monitor
Protocol Monitor is the easiest way to see the actual CDP request and response without writing a client.
- Open Chrome DevTools.
- Open DevTools settings, choose Experiments, and enable Protocol Monitor if it is not already available.
- Open the Command Menu, search for Protocol monitor, and open it.
- Choose the page target you want to control.
- Use the command editor to select
Page.captureScreenshotand enter parameters such as{"format":"png"}. - Send the command and inspect the response. The
dataproperty contains the image as base64 text.
The official DevTools guide also demonstrates sending protocol commands from DevTools itself with Main.MainImpl.sendOverProtocol. That route is useful for experimenting with a command before putting it into an automation script.
Option 2: Send Page.captureScreenshot from code
Every CDP message has an integer identifier, a method name, and optional parameters. The response with the matching identifier contains the result. The central request is:
{"id":1,"method":"Page.captureScreenshot","params":{"format":"png"}}Enable the Page domain when your client workflow requires it:
{"id":2,"method":"Page.enable"}Then decode result.data. The protocol specifies the encoding, but not your language’s file-writing API.
Python example using a CDP WebSocket
Install a WebSocket client first:
python -m pip install websocket-client requestsThe following script discovers the first page target, connects to its WebSocket endpoint, enables the Page domain, captures a PNG, and writes it to disk.
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import base64
import json
import requests
import websocket
TARGETS = "http://127.0.0.1:9222/json"
target = next(t for t in requests.get(TARGETS, timeout=10).json()
if t.get("type") == "page")
ws = websocket.create_connection(target["webSocketDebuggerUrl"], timeout=30)
def call(message_id, method, params=None):
payload = {"id": message_id, "method": method}
if params is not None:
payload["params"] = params
ws.send(json.dumps(payload))
while True:
response = json.loads(ws.recv())
if response.get("id") == message_id:
if "error" in response:
raise RuntimeError(response["error"])
return response["result"]
call(1, "Page.enable")
result = call(2, "Page.captureScreenshot", {"format": "png"})
with open("page.png", "wb") as image:
image.write(base64.b64decode(result["data"]))
ws.close()
print("Wrote page.png")In production, match responses by id because CDP can emit asynchronous events between your request and its response. Add navigation and readiness checks before capture when the page is dynamic.
Node.js example using the Chrome DevTools Protocol directly
This example uses Node’s built-in HTTP and WebSocket support only if your Node version provides a WebSocket implementation. Otherwise install a compatible WebSocket package and import it as required by that package.
const http = require('node:http');
const fs = require('node:fs');
function getJson(url) {
return new Promise((resolve, reject) => {
http.get(url, res => {
let body = '';
res.on('data', chunk => body += chunk);
res.on('end', () => resolve(JSON.parse(body)));
}).on('error', reject);
});
}
(async () => {
const targets = await getJson('http://127.0.0.1:9222/json');
const page = targets.find(t => t.type === 'page');
if (!page) throw new Error('No page target found');
const ws = new WebSocket(page.webSocketDebuggerUrl);
await new Promise((resolve, reject) => {
ws.addEventListener('open', resolve, { once: true });
ws.addEventListener('error', reject, { once: true });
});
let nextId = 1;
function call(method, params) {
const id = nextId++;
return new Promise((resolve, reject) => {
function onMessage(event) {
const message = JSON.parse(event.data);
if (message.id !== id) return;
ws.removeEventListener('message', onMessage);
if (message.error) reject(new Error(JSON.stringify(message.error)));
else resolve(message.result);
}
ws.addEventListener('message', onMessage);
ws.send(JSON.stringify({ id, method, params }));
});
}
await call('Page.enable');
const result = await call('Page.captureScreenshot', { format: 'png' });
fs.writeFileSync('page.png', Buffer.from(result.data, 'base64'));
ws.close();
})();Capture formats and compression
PNG
PNG is the documented default and preserves lossless image data. Use it for text, diagrams, UI regression checks, or further image processing.
JPEG
Set format to jpeg. The documented quality integer range is 0–100 and applies to JPEG encoding; it is not a PNG quality control.
{"id":1,"method":"Page.captureScreenshot","params":{"format":"jpeg","quality":80}}WebP
Set format to webp when your consumers support it. Choose the format based on compatibility and file-size requirements rather than assuming one format is always smaller.
Faster encoding
optimizeForSpeed:true requests faster encoding at the cost of a larger resulting image. Its documented default is false.
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Capture a viewport, region, or full page
Default viewport screenshot
With no clip and no beyond-viewport request, capture the visible page area using the current browser metrics:
{"id":1,"method":"Page.captureScreenshot","params":{"format":"png"}}Capture a rectangular region with clip
Pass a clip object containing x, y, width, height, and scale. These coordinates and dimensions are in device-independent pixels.
{"id":1,"method":"Page.captureScreenshot","params":{"format":"png","clip":{"x":100,"y":200,"width":800,"height":600,"scale":1}}}Keep the rectangle inside the rendered content you intend to capture. A non-unit scale changes the output pixel dimensions without changing the CSS-coordinate rectangle.
Capture beyond the viewport
Set captureBeyondViewport:true to request content outside the current viewport:
{"id":1,"method":"Page.captureScreenshot","params":{"format":"png","captureBeyondViewport":true}}The tip-of-tree reference documents this field with a default of false and marks it experimental. Full-page output can use the page’s actual content size rather than the nominal viewport dimensions, so inspect the resulting image dimensions instead of assuming a fixed height. Support and behavior can differ between Chrome versions.
Surface capture
fromSurface controls whether the image is captured from the surface rather than the view. Its documented default is true. Do not assume identical output across every emulation or platform configuration.
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- 【Ultra Low Latency Screen Sharing】Built with a premium aluminum alloy shell and advanced chipset for stable heat dissipation, ensuring ultra-low latency transmission. Capture high-quality video and dual-channel audio in real time—no lag, no frame drop—ideal for Twitch, YouTube, or OBS streaming.
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- 【Wide Compatibility & Multi-Device Support】Compatible with Windows 7 8 10 11, macOS, Linux,Android and supports most popular software such as OBS, Zoom, VLC, Twitch Studio, and more. Works seamlessly with PS4, PS5, Xbox, Switch, DSLR cameras, TV boxes, and other HDMI-output devices for streaming to YouTube, Twitch, etc.
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Set viewport and device metrics before capture
Screenshot pixels reflect the page’s current layout and device metrics. For a mobile-style capture, send Emulation.setDeviceMetricsOverride first, then capture:
{"id":3,"method":"Emulation.setDeviceMetricsOverride","params":{"mobile":true,"width":390,"height":844,"deviceScaleFactor":3}}
{"id":4,"method":"Page.captureScreenshot","params":{"format":"png"}}The official DevTools example uses mobile, width, height, and deviceScaleFactor. Those values are an example configuration, not a universal device preset. Clear the override after your test if the same target will be reused:
{"id":5,"method":"Emulation.clearDeviceMetricsOverride"}Set the viewport before navigation when responsive breakpoints, lazy loading, or layout scripts depend on the initial size.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Make captures reliable on real pages
Wait for navigation and rendering
A successful protocol response does not prove that fonts, images, client-rendered components, or data requests have finished. Wait for a navigation lifecycle event, a known DOM condition, or an application-specific readiness signal before calling Page.captureScreenshot.
Handle lazy content
Full-page capture may not trigger every site’s lazy-loading strategy. Scroll or use page JavaScript to reveal required content, then wait for images and layout to settle. Verify the resulting dimensions and inspect the image rather than treating a completed command as proof of completeness.
Control animations
Animations and blinking carets can make repeated captures differ. Inject CSS or application state that disables transitions where your test permits it, and capture at a deterministic point in time.
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Use the correct target
The /json endpoint can return tabs, extensions, workers, and other targets. Select the page target whose URL and type match your intended document; connecting to a worker does not provide the page screenshot domain you expect.
Common errors and fixes
| Symptom | Likely cause | Fix |
|---|---|---|
| Connection refused on port 9222 | Chrome was not started with remote debugging, or the port is different. | Launch the intended Chrome binary with a localhost debugging port and verify the /json endpoint. |
| No page target found | The target list contains only workers, extensions, or a blank browser session. | Open the page, select an entry with type equal to page, and confirm its WebSocket URL. |
| “Method not found” | The connected target is not a page, or the Chrome build does not expose the method as expected. | Reconnect to a page target and check the protocol definition bundled with that Chrome version. |
| Image is blank or incomplete | Capture occurred before navigation, client rendering, fonts, or lazy resources completed. | Wait for a deterministic readiness condition, allow resources to settle, and capture again. |
| JPEG quality rejected | quality was supplied with PNG or outside 0–100. |
Use quality only with JPEG and keep it in the documented 0–100 range. |
| Full-page height is unexpected | Actual content size differs from the nominal viewport, or the experimental field behaves differently in that Chrome build. | Inspect output dimensions, verify layout and lazy loading, and test against the target Chrome version. |
| Decoded file cannot be opened | The base64 text was written directly instead of decoded. | Base64-decode result.data and write binary bytes. |
| Responses appear out of order | CDP events and responses share the same WebSocket. | Route messages by their numeric id and handle event messages separately. |
Performance, output size, and compatibility
- PNG preserves detail but can be large; JPEG quality trades fidelity for size; WebP is another supported output choice.
optimizeForSpeedcan reduce encoding latency while increasing output size.- Large full-page images consume memory in Chrome and in your client while base64 is in transit. Stream or process jobs one at a time when pages are very tall.
- Use clipping when you need one component rather than an entire document.
- Experimental parameters and implementation details can vary by Chrome release. Pin or record the browser version in automated tests and verify behavior after upgrades.
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FAQ
Does Page.captureScreenshot return an image file?
No. It returns base64-encoded image data in the response’s data field. Your client writes the decoded bytes to a file or sends them elsewhere.
Can I use CDP screenshots for a PDF?
Page.captureScreenshot produces an image. For a paginated document, use the separate CDP print-to-PDF workflow or a service that exposes PDF capture.
Are CDP parameters identical in every Chrome release?
No. The tip-of-tree protocol reference can include experimental fields whose availability and behavior differ by browser version. Check the protocol definition for the Chrome build you run.
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