To make a website download a screenshot when a visitor clicks a button, first determine where the pixels come from. If they are already in a canvas, export the canvas with toBlob(), create a temporary object URL, and trigger an anchor with a download filename. If you need the actual browser display, use getDisplayMedia(); the browser will require the visitor to choose a tab, window, or screen and approve capture. If the target is an arbitrary URL or a server-rendered page, use browser automation or a hosted screenshot service instead of client-side download code.
Download an image that is already rendered in a canvas
This is the simplest and most reliable website implementation. It works for drawing apps, chart exporters, canvas games, image editors, and any page that already owns the pixels in an HTMLCanvasElement.
Minimal PNG download
<button id="downloadScreenshot" type="button">Download screenshot</button>
<canvas id="preview" width="1200" height="800"></canvas>
<script>
const canvas = document.querySelector('#preview');
const button = document.querySelector('#downloadScreenshot');
button.addEventListener('click', () => {
canvas.toBlob((blob) => {
if (!blob) {
throw new Error('Could not encode the screenshot');
}
const url = URL.createObjectURL(blob);
const link = document.createElement('a');
link.href = url;
link.download = 'screenshot.png';
link.textContent = 'Save screenshot.png';
link.click();
// Keep the URL alive while the generated file is still usable.
setTimeout(() => URL.revokeObjectURL(url), 1000);
}, 'image/png');
});
</script>toBlob() encodes the canvas asynchronously. PNG support is required, and PNG is also the fallback when an unsupported or omitted type is requested. The anchor’s download value is a suggested filename, not a command that can override browser settings. A browser may save automatically, ask the visitor where to save, or open the resource according to its configuration.
Offer JPEG or WebP
Pass a MIME type and, for lossy formats, a quality value between 0 and 1:
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canvas.toBlob((blob) => {
if (!blob) return;
const url = URL.createObjectURL(blob);
const link = document.createElement('a');
link.href = url;
link.download = 'screenshot.webp';
link.click();
// Revoke after the link is no longer needed.
setTimeout(() => URL.revokeObjectURL(url), 1000);
}, 'image/webp', 0.9);Use PNG when text, line art, transparency, or exact pixel reproduction matters. JPEG is appropriate for photographic content but does not preserve transparency. WebP can reduce file size when the visitor’s browser supports it; retain a PNG fallback if format compatibility is important.
Keep a visible link when another click may be required
Some browsers or download policies may not complete a synthetic click exactly as expected. For generated files that should remain available, append a visible link instead of immediately removing it:
canvas.toBlob((blob) => {
if (!blob) return;
const url = URL.createObjectURL(blob);
const link = document.createElement('a');
link.href = url;
link.download = 'screenshot.png';
link.textContent = 'Download the screenshot';
document.querySelector('#downloads').replaceChildren(link);
// Revoke only when you remove the link from the interface.
}, 'image/png');Why toBlob() is preferable to toDataURL()
toDataURL() turns the whole image into a long string. Large canvases can consume considerable memory, create expensive string copies, and run into URL-length limits. toBlob() produces binary data and an object URL, which is a better fit for large screenshots. Release each object URL with URL.revokeObjectURL() after the user can no longer open or save that file; revoking it immediately after click() can make the download unreliable.
Capture the live browser display with getDisplayMedia()
Use the Screen Capture API when the required image is the pixels currently displayed in a selected tab, window, or monitor rather than content your page has drawn itself. This is not a silent screenshot function. The browser presents a source picker, requires permission, and may reject calls that are not made after a recent user interaction. It also requires a secure context such as HTTPS, and availability varies by browser and device.
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Capture one frame and download it
async function captureDisplayFrame() {
const stream = await navigator.mediaDevices.getDisplayMedia({
video: true,
audio: false
});
const track = stream.getVideoTracks()[0];
try {
const imageCapture = new ImageCapture(track);
const bitmap = await imageCapture.grabFrame();
const canvas = document.createElement('canvas');
canvas.width = bitmap.width;
canvas.height = bitmap.height;
canvas.getContext('2d').drawImage(bitmap, 0, 0);
canvas.toBlob((blob) => {
if (!blob) throw new Error('Could not encode the captured frame');
const url = URL.createObjectURL(blob);
const link = document.createElement('a');
link.href = url;
link.download = 'display-screenshot.png';
link.textContent = 'Download display screenshot';
document.querySelector('#downloads').replaceChildren(link);
// Keep the URL while the visible link remains available.
}, 'image/png');
bitmap.close();
} finally {
stream.getTracks().forEach((captureTrack) => captureTrack.stop());
}
}
document.querySelector('#captureDisplay').addEventListener('click', () => {
captureDisplayFrame().catch((error) => {
console.error(error);
// Show a cancel, permission, or unsupported-browser message in the UI.
});
});Call this function from a clearly labeled button. Explain what will be captured and provide a cancel path. The visitor chooses the source; a site cannot use constraints to silently narrow that choice. Do not confuse this ordinary webpage API with extension-only tab-capture capabilities or browser DevTools commands.
When canvas export fails: origin-clean rules
A canvas becomes tainted when it contains pixels from another origin that were loaded without permission for readback. Once tainted, calls such as toBlob() and toDataURL() throw a SecurityError. Configure the remote server to send suitable CORS response headers and request the image with the matching cross-origin mode before drawing it:
const image = new Image();
image.crossOrigin = 'anonymous';
image.onload = () => {
const canvas = document.querySelector('#preview');
canvas.getContext('2d').drawImage(image, 0, 0);
};
image.src = 'https://assets.example.com/photo.png';The server at assets.example.com must explicitly permit your page’s origin (or use an appropriate public CORS policy). Setting crossOrigin in JavaScript cannot create permission that the server did not grant.
Why a direct URL usually cannot be downloaded as a website screenshot
An anchor can suggest downloading a same-origin HTTP resource or a generated blob: or data: URL. It cannot force an arbitrary cross-origin page URL to become a screenshot. A URL such as https://example.com is HTML, not a bitmap, and browser security rules prevent a normal page from reading another site’s rendered pixels.
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Choose one of these architectures instead:
- Your own page: render the content into a canvas and export that canvas.
- Visitor’s current display: request
getDisplayMedia()and let the visitor select a source. - Arbitrary URL or HTML: run a browser automation worker or call a hosted screenshot endpoint. This is suitable for previews, reports, monitoring, and server-side jobs.
- Manual development work: use browser DevTools. Firefox, for example, documents saving screenshots of selected nodes; this is a developer workflow, not a feature silently available to site visitors.
Performance and reliability checklist
- Use
toBlob()rather than building large data URLs. - Choose an output format and dimensions appropriate to the use case; a very large canvas can require substantial memory during encoding.
- Disable the capture button or show progress while an asynchronous encode is running, so users do not start duplicate jobs.
- Keep the generated object URL alive for every visible link and revoke it when that link is removed.
- Handle a null Blob and display an actionable error instead of assuming encoding succeeded.
- Expect browser prompts and settings to affect filenames and save behavior.
- For display capture, test secure-context requirements, permission denial, source-picker cancellation, and unsupported browsers.
- Never promise identical behavior across desktop, mobile, and every browser without testing the exact target matrix.
Common errors and fixes
“SecurityError” from toBlob()
The canvas is not origin-clean, usually because a remote image or video lacked CORS permission. Configure response headers on the asset server, set crossOrigin before assigning src, and redraw onto a fresh canvas after the policy is corrected.
The download opens instead of saving
The download attribute is a hint. Browser preferences, content-disposition headers, and security policy can change the result. Keep a visible same-origin or Blob link and tell users where the browser may save the file.
The generated file is empty or corrupt
Wait for the toBlob() callback, check for a null Blob, and do not revoke the object URL until the link is no longer usable. If the canvas is still being drawn, export only after rendering completes.
getDisplayMedia() rejects immediately
Make the call from a recent user gesture, serve the page over HTTPS, verify that the browser supports the API, and distinguish cancellation from permission denial in your error message.
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Only part of the page appears
Canvas export captures the canvas bitmap, not the surrounding DOM. Display capture captures the selected visible surface, not an automatically expanded, full-length webpage. For a full-page URL image, use a server-side browser or screenshot service.
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When the input is a URL rather than an image already in your page, ScreenshotNeo provides a website screenshot API and MCP server. One GET request returns PNG, JPEG, WebP, or PDF. It accepts cookies and consent banners like a visitor, then removes more than 60 known consent platforms, newsletter popups, and chat widgets before capture; each cleanup step can be disabled. Bot checks or CAPTCHAs, blank pages, timeouts, failed loads, and cache hits are not billed, and response headers identify the page verdict and billing status.
See the complete parameter reference in the ScreenshotNeo documentation. A basic cURL request is:
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,
)
r.raise_for_status()
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}`);
if (!res.ok) throw new Error(`Screenshot failed: ${res.status}`);
const data = Buffer.from(await res.arrayBuffer());
await import('node:fs/promises').then(fs => fs.writeFile('shot.webp', data));For AI workflows, its MCP server exposes take_screenshot, get_page_info, and capture_pdf to Claude, Cursor, and other MCP clients. Other useful options include full-page lazy-image loading, CSS-selector element capture, dark mode, device presets and custom viewports, retina scale, PDF paper and page controls, custom CSS and JavaScript, clicks, selector or network-idle waits, ad and tracker blocking, custom headers, cookies, user agents, authorization, timezone and geolocation, transparent backgrounds, resizing, configurable caching, signed public-image links, asynchronous webhooks, bulk capture of up to 100 URLs per call, a usage API, and an OpenAPI specification. Parameter names used by other screenshot APIs also work, which can simplify migration.
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Frequently Asked Questions
Can JavaScript take a screenshot of any webpage without permission?
No. A page can export pixels it owns, or request a user-approved display capture. An arbitrary URL requires a server-side browser or screenshot service.
Should I use PNG, JPEG, or WebP?
Use PNG for text, line art, and transparency; JPEG for photographs without transparency; WebP when smaller files are useful and your compatibility requirements allow it.
Why does my downloaded filename differ from the value in link.download?
The property is a filename suggestion. Browser preferences, prompts, and response headers can influence the final name and handling.
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