Start without either parameter. Render the page with your screenshot service’s defaults, then add a short ms_delay only when asynchronous content is missing. Set device_scale: 1 for the smallest practical image, or 2 when you need a retina-density result. A delay changes when the capture occurs; device scale changes how many output pixels are produced.
What the two parameters actually do
ms_delay is a post-load pause
ms_delay tells the renderer to wait an additional number of milliseconds after its normal page-loading work before it captures the image. It is useful when JavaScript, remote images, web fonts, embeds, canvas drawing, or animations finish after the initial load signal.
HTML/CSS to Image advises using it only when expected content is missing, dynamic content does not appear, or custom fonts and images fail to load. Its documentation also says most users do not need it because the service handles common loading cases automatically. Treat the setting as a targeted fix, not a default for every request.
device_scale changes output pixels
device_scale multiplies the rendered pixel density while preserving the page’s CSS dimensions. A 1,200 × 630 canvas rendered with device_scale: 2 becomes a 2,400 × 1,260 image. Text and vector-like elements can look sharper at higher density, but the file is larger and takes longer to transfer and process.
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| Setting | Changes | Typical reason to use it | Cost |
|---|---|---|---|
ms_delay |
Capture timing | Wait for late JavaScript, images, fonts or embeds | Longer processing time |
device_scale |
Output pixel dimensions | Choose normal or retina-density output | Larger files, storage and delivery |
A reliable tuning procedure
- Make a baseline capture. Use provider defaults, with no extra delay and a scale of 1 if that is the documented default. Save the image and note its dimensions.
- Identify what is missing. Check whether the problem is a late-rendering component, a blocked resource, a selector that never appears, or a genuinely blank/error page. A delay cannot repair a failed request or a bot check.
- Add a small delay. Start with 100–500 ms. Canvasflare documents a 100 ms default and suggests beginning at 500 ms when blank images occur; those figures are examples, not a universal optimum.
- Increase gradually. Add time in small increments and stop as soon as the required content appears. A longer wait increases latency on every request.
- Prefer a readiness condition when available. If the page has a stable selector such as
#report-ready, wait for that selector rather than guessing a large blind delay. - Select output density separately. Keep
device_scale: 1for ordinary web previews and lower transfer costs. Try2for retina displays, print-like graphics or small text, then verify the resulting dimensions and file size. - Test several page states. A delay that fixes one route may be excessive for another. Record the URL, viewport, scale, delay and whether the target content appeared.
Using ms_delay in HTML/CSS to Image
The parameter name in this section is specific to HTML/CSS to Image. Follow that provider’s request format and pass an integer number of milliseconds. For example, a request body might contain:
{"url":"https://example.com/dashboard","ms_delay":500,"device_scale":1}Use 500 only as a starting test for content that arrives late. If 500 ms is enough, do not automatically increase it to several seconds. If the page has an explicit readiness selector, use that provider’s wait-for-selector feature instead and leave ms_delay at zero.
When a delay will not help
- The URL redirects to a login page or requires credentials you did not provide.
- A bot check or CAPTCHA prevents the real page from loading.
- JavaScript throws an error, an API request returns an error, or a resource is blocked by policy.
- The selector or content is inside a cross-origin frame that the service cannot access.
- The page is intentionally blank at the requested route.
Inspect the rendered page or page-information endpoint, if your provider offers one, before increasing the delay indefinitely.
Choosing the right device_scale
Use scale 1 for normal delivery
Scale 1 keeps the output close to the CSS viewport’s pixel dimensions. It is the sensible choice for dashboards, link previews, monitoring thumbnails and high-volume jobs where file size and throughput matter more than maximum density.
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Scale 2 doubles each dimension, so total pixel count is four times the scale-1 result. It is useful when an image will be displayed at half its native pixel dimensions on a retina screen, or when small labels must remain legible. Check your object-storage, CDN and downstream image-processing limits before enabling it broadly.
Do not confuse scale with viewport size
Viewport width controls the responsive layout. Device scale controls the number of raster pixels used to represent that layout. Increasing scale does not make a desktop layout appear at a wider CSS width, and it does not reveal content hidden by responsive breakpoints.
Equivalent controls in other screenshot APIs
Do not copy parameter names between vendors without checking their reference. ScreenshotAPI calls the same concepts delay and deviceScaleFactor; its documented ranges are 0–20,000 milliseconds for delay and 1–5 for device scale factor. A request accepted by one service can be rejected or silently ignored by another.
| Concept | HTML/CSS to Image | Canvasflare description | ScreenshotAPI |
|---|---|---|---|
| Extra wait | ms_delay |
Additional delay for JavaScript completion; documentation example uses 100 ms default and 500 ms starting point for blank images | delay, 0–20,000 ms |
| Pixel density | device_scale |
Not stated in the cited description | deviceScaleFactor, 1–5 |
| Readiness selector | Use the provider’s wait/selector option when available | Not stated | Not stated in the cited material |
There is no independent benchmark establishing one universally optimal delay or scale. Measure your own pages and choose the smallest settings that meet the visual requirement.
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Complete examples
HTML/CSS to Image request pattern
curl -X POST https://hcti.io/v1/image
-u YOUR_USER_ID:YOUR_API_KEY
-H 'Content-Type: application/json'
-d '{"url":"https://example.com/report","ms_delay":500,"device_scale":2}'The endpoint and authentication shown above are illustrative of the parameter payload; use the exact endpoint and authentication documented by your account. Keep the vendor name beside copied examples because another API may require delay or deviceScaleFactor instead.
Automating a delay/scale test in Python
import requests
url = "https://example.com/report"
for delay in (0, 250, 500, 750):
payload = {"url": url, "ms_delay": delay, "device_scale": 1}
response = requests.post("YOUR_PROVIDER_ENDPOINT", json=payload, timeout=90)
response.raise_for_status()
with open(f"report-{delay}ms.png", "wb") as image:
image.write(response.content)
What to log in production
- URL and viewport or device preset.
- Delay and device scale actually sent.
- HTTP status, response time and output dimensions.
- Whether the expected selector or text was present.
- File size and any provider verdict, cache or failure headers.
Troubleshooting blank or incomplete screenshots
The image is blank
First verify the URL manually and check redirects, authentication and bot protection. Then try a 500 ms delay. If the page remains blank, inspect console/network diagnostics or the provider’s page-info result; a failed load cannot be fixed by waiting.
Dynamic data is missing
Confirm that the data request has completed and that the page does not require a click, scroll or consent action. Add a short delay, or wait for a stable ready selector. For lazy-loaded content, use the provider’s full-page or scroll behavior where available.
Fonts look wrong
Check that font files are reachable from the rendering environment and that cross-origin headers permit loading. A short delay can allow a slow custom font to finish, but it cannot repair a 404 or blocked font.
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The image is unexpectedly huge
Inspect both viewport dimensions and device scale. Scale 2 produces four times as many pixels as scale 1 for the same CSS rectangle. Reduce the scale, resize after capture, or deliver a smaller derivative.
A parameter is ignored or rejected
Check the provider’s spelling, numeric range and request location. HTML/CSS to Image uses ms_delay and device_scale; ScreenshotAPI documents delay and deviceScaleFactor. Unsupported fields may be ignored or return a validation error.
Performance, reliability and cost considerations
- Latency: Every additional millisecond is part of the critical path. Use readiness conditions for predictable pages and reserve long delays for genuinely asynchronous work.
- Throughput: Higher scales increase encoding and transfer time. Batch or queue high-density jobs instead of applying scale 2 to every thumbnail.
- Reliability: Cache stable pages where permitted, but do not mistake a cached old image for proof that a new delay works. Test after content changes.
- Validation: Compare dimensions and file size in monitoring, not just HTTP success. A successful response can still represent an error page or an incomplete state.
- Cost: Provider billing rules differ. A larger image or longer render may consume more resources even when the API charges per request; check your plan’s terms.
Or skip the browser setup
ScreenshotNeo is a website screenshot API and MCP server. It accepts consent banners before capture and removes more than 60 known consent platforms, newsletter popups and chat widgets. Bot checks, CAPTCHAs, blank pages, timeouts, failed loads and cache hits are not billed; each response identifies the page verdict and billing status in X-Page-Verdict and X-Billed headers. Its MCP server provides take_screenshot, get_page_info and capture_pdf tools for Claude, Cursor and other MCP clients.
One GET request returns a PNG, JPEG, WebP or PDF:
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Frequently Asked Questions
Should I always set ms_delay to 500 ms?
No. Five hundred milliseconds is a practical starting test cited by Canvasflare for blank images, not a universal requirement. Use the shortest delay that consistently captures your page.
Does device_scale change CSS breakpoints?
No. Breakpoints respond to the CSS viewport. device_scale changes raster pixel density after the layout is selected.
Can a delay fix a CAPTCHA?
No. Waiting longer does not solve bot protection, authentication failures or blocked network requests.
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