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Use Playwright to read URLs from a file, capture each page in one reusable browser process, and flag screenshots whose pixels show unusually little variation. Treat that flag as a review candidate—not proof of a failed page: a plain or intentionally empty page can also look uniform. The script below records navigation failures separately from image findings.
What the workflow can—and cannot—tell you
A batch capture has two distinct results to track: whether the browser loaded and captured the page, and whether the resulting image looks unusually uniform. A navigation error or timeout is not the same as a valid screenshot that happens to contain a blank-looking page.
Playwright’s Page API supports navigation and screenshots saved to a file, full-page capture, and screenshot bytes for further processing (Playwright Page API; Playwright screenshot documentation). The pixel-variation check below is a practical heuristic, not a built-in Playwright blank-page classifier. Playwright does not prescribe a universal score or cutoff for blank images.
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The example uses Node.js, Playwright, and the sharp image library. It reads one URL per line from urls.txt, writes images and a JSONL results file, and continues after individual navigation errors.
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- Install a current Node.js release if it is not already available.
- In a new project directory, run
npm init -y. - Install dependencies with
npm install playwright sharp. - Install Playwright’s Chromium browser with
npx playwright install chromium. - Create
urls.txt, putting one complete URL on each line. Lines beginning with#and empty lines are ignored.
Capture the URL list and flag low-variation images
Save this as bulk-screenshot.js. By default, it captures each page’s visible viewport. Set FULL_PAGE=1 to capture the full scrollable page. The example uses a simple luminance standard deviation across sampled pixels; its initial cutoff is a starting point to calibrate against your pages, not a universal threshold.
const fs = require('node:fs/promises');
const path = require('node:path');
const { chromium } = require('playwright');
const sharp = require('sharp');
const inputFile = process.argv[2] || 'urls.txt';
const outputDir = process.env.OUTPUT_DIR || 'screenshots';
const fullPage = process.env.FULL_PAGE === '1';
const timeoutMs = Number(process.env.NAV_TIMEOUT_MS || 30000);
const blankStddevThreshold = Number(process.env.BLANK_STDDEV || 3);
async function luminanceStats(buffer) {
const { data, info } = await sharp(buffer)
.flatten({ background: '#ffffff' })
.resize({ width: 200, height: 200, fit: 'inside' })
.removeAlpha()
.raw()
.toBuffer({ resolveWithObject: true });
const values = [];
for (let i = 0; i < data.length; i += info.channels) {
const r = data[i], g = data[i + 1], b = data[i + 2];
values.push(0.2126 * r + 0.7152 * g + 0.0722 * b);
}
const mean = values.reduce((sum, value) => sum + value, 0) / values.length;
const variance = values.reduce((sum, value) => sum + (value - mean) ** 2, 0) / values.length;
return { meanLuminance: Number(mean.toFixed(2)), luminanceStddev: Number(Math.sqrt(variance).toFixed(2)) };
}
(async () => {
await fs.mkdir(outputDir, { recursive: true });
const lines = (await fs.readFile(inputFile, 'utf8')).split(/r?n/);
const urls = lines.map(line => line.trim()).filter(line => line && !line.startsWith('#'));
const resultsPath = path.join(outputDir, 'results.jsonl');
const results = await fs.open(resultsPath, 'w');
const browser = await chromium.launch({ headless: true });
const context = await browser.newContext({ viewport: { width: 1440, height: 1000 } });
try {
for (let index = 0; index < urls.length; index++) {
const url = urls[index];
const id = String(index + 1).padStart(4, '0');
const record = { id, url, capturedAt: new Date().toISOString(), fullPage };
const page = await context.newPage();
try {
const response = await page.goto(url, { waitUntil: 'domcontentloaded', timeout: timeoutMs });
record.finalUrl = page.url();
record.httpStatus = response ? response.status() : null;
const imagePath = path.join(outputDir, `${id}.png`);
const buffer = await page.screenshot({ path: imagePath, fullPage, animations: 'disabled' });
const metadata = await sharp(buffer).metadata();
record.screenshot = imagePath;
record.width = metadata.width;
record.height = metadata.height;
Object.assign(record, await luminanceStats(buffer));
record.blankCandidate = record.luminanceStddev < blankStddevThreshold;
record.outcome = record.blankCandidate ? 'captured_low_variation_review' : 'captured';
} catch (error) {
record.outcome = 'navigation_or_capture_error';
record.error = String(error.message || error);
record.finalUrl = page.url();
} finally {
await page.close();
}
await results.write(`${JSON.stringify(record)}n`);
console.log(`${record.id} ${record.outcome} ${record.url}`);
}
} finally {
await context.close();
await browser.close();
await results.close();
}
})().catch(error => {
console.error(error);
process.exitCode = 1;
});Run it with node bulk-screenshot.js urls.txt. To capture full pages, use FULL_PAGE=1 node bulk-screenshot.js urls.txt. Images are named by input order, such as 0001.png; screenshots/results.jsonl contains one record per input URL, including timestamp, final URL, HTTP status when available, dimensions, detector values, and outcome. A successful capture with an HTTP error status is still recorded as a capture; inspect the status and page content according to your needs.
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Understand and calibrate the blank-candidate rule
The script shrinks each image to at most 200 pixels on each side and calculates the standard deviation of sampled luminance values. When that variation is below BLANK_STDDEV, it marks the record for review. The default value of 3 is merely an initial setting in this example; no universal cutoff is established.
- Review representative pages before processing a large list: typical content, an intentionally plain page, a loading or error state, a consent screen, a dark page, and pages with mostly solid-color branding.
- Compare flagged and unflagged samples, then adjust the cutoff for your own pages with
BLANK_STDDEV=VALUE. - Low variation can mean an intentional design, a blocked or incomplete page, or a viewport that misses the page’s content. It is a prompt to inspect the image, not an automated verdict.
- Full-page captures can behave differently from viewport captures: they include more content, create larger images, and can change the variation score. Keep capture mode consistent when comparing results.
Choose capture settings for the job
Viewport or full page
Viewport screenshots are faster and smaller, but can miss content below the fold. Full-page screenshots include the scrollable page and are useful when the target content may appear lower down; they can take more resources and alter the blankness heuristic’s result.
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Navigation readiness and dynamic content
The example waits for domcontentloaded so it does not depend on every network request finishing. This is useful for pages with analytics or long-lived requests, but a page that renders its main content later may be captured too early. If that happens, use a site-specific readiness condition such as a selector wait or a deliberate delay before taking the screenshot. Avoid treating a fixed delay as proof that all content is ready.
Repeatability and visual regression
Keep browser version, operating system, viewport, scale, headless mode, and machine conditions consistent when image results need to be comparable. Playwright notes that rendering can vary with host OS, browser version and settings, hardware, power source, and headless mode (Playwright visual comparisons).
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If every URL has a trusted expected image and your goal is to detect visual changes rather than discover blankness, Playwright Test’s toHaveScreenshot() is a different tool for the job. It waits until two consecutive screenshots match before comparing against the expected snapshot, and offers image-difference controls. It does not provide a generic blank-image detector. See the PageAssertions options.
Handle larger batches responsibly
This script reuses one browser and context but opens and closes a page for each URL sequentially. That keeps resource usage simpler and makes the first run easier to diagnose. For very large lists, runtime grows with page load and capture time; introduce a small, controlled number of concurrent pages only after measuring memory and stability on your own machines. Too much concurrency can increase timeouts and incomplete renders.
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Retain the JSONL manifest alongside images so you can identify which input produced each file and distinguish browser failures from low-variation images. If you rerun a list, preserve the same input ordering or use URL-derived stable IDs in your own workflow to make comparisons easier. There is no general performance figure or blank-detection accuracy guaranteed by Playwright for this custom implementation.
Troubleshooting
- Chromium executable is missing: run
npx playwright install chromiumin the project and retry. - A URL fails immediately: make sure each non-comment line is a complete URL with a scheme such as
https://; inspect the recorded error and final URL. - Navigation timeout: some pages never reach the chosen readiness state or respond slowly. Increase
NAV_TIMEOUT_MSfor the run, or choose a more suitable readiness strategy for that site. A timeout is recorded as an error, not a blank screenshot. - Images are blank although the page loads: the site may render content after
domcontentloaded. Wait for the relevant content selector or a site-appropriate delay before capture, then check whether the page requires authentication or blocks automated browsers. - Too many false blank flags: lower or otherwise recalibrate
BLANK_STDDEVusing reviewed examples. Uniform backgrounds, sparse layouts, and intentionally simple pages can have low variation. - Missed blank pages: a page can be mostly uniform while containing a small meaningful region that affects the score. Review the images and consider additional checks suited to your content, rather than assuming one global pixel threshold is sufficient.
- Images differ between runs: standardize browser and machine settings and account for animations, dynamic content, time-dependent text, and rotating content. The example disables animations during screenshot capture, but cannot make a changing site deterministic.
- Memory use rises on long pages: try viewport capture, reduce concurrency if you added it, and process a manageable number of URLs per run.
Or skip the browser setup
ScreenshotNeo can return a screenshot from one request; its clean-shot steps accept cookie or consent banners and remove more than 60 known consent platforms, newsletter popups, and chat widgets, with each step configurable. It bills only clean shots: bot checks or CAPTCHAs, blank pages, timeouts, failed loads, and cache hits cost nothing, and responses identify outcomes with X-Page-Verdict and X-Billed headers. It also provides an MCP server with screenshot, page-info, and PDF tools for AI agents. The service includes 1,000 screenshots a month free with no card; paid plans start at $5 for 3,000 shots. Its response headers identify blank-page outcomes, but the pixel-variation heuristic above is still useful when you want to inspect and classify saved image files yourself.
Use the following cURL request, substituting your target URL and API key. See the ScreenshotNeo API documentation for parameters and response details.
curl -G "https://api.screenshotneo.com/v1/shot" -d access_key=YOUR_API_KEY --data-urlencode url=https://stripe.com -o shot.webpSign up for ScreenshotNeo to get 1,000 screenshots a month free with no card.
Frequently Asked Questions
Does Playwright provide a built-in blank screenshot detector?
No. The pixel-variation check in the example is custom logic, and its threshold must be calibrated for the pages being captured.
Should I use a visual snapshot assertion to find blank pages?
Use visual assertions when you have trusted expected images and want to detect changes. They compare against a baseline; they are not a generic blank-image classifier.
Quick Recap
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