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Use the User-Agent field or option documented by the screenshot tool you chose; there is no universal parameter name or request format. For example, Screenshot APIs accepts user_agent in a JSON body, ScreenshotCenter documents a user_agent query parameter, and the command-line tool shot-scraper uses --user-agent. Check the captured page afterward: a successful image response does not necessarily mean the target content loaded.
Put the User-Agent where your provider expects it
A User-Agent is a string sent with a request to identify the client. Screenshot services expose it through different interfaces, so do not assume a field accepted by one service works with another. The documented examples below illustrate three distinct patterns.
Screenshot APIs: send user_agent in the JSON body
Screenshot APIs documents POST /v1/screenshot with a user_agent string in the JSON request body. Supply either url or html. Its API reference shows API-key authentication with an X-Api-Key header; bearer-token authentication is also documented. See the Screenshot APIs reference for the provider’s current request details.
curl -X POST https://screenshotapis.org/v1/screenshot
-H "X-Api-Key: YOUR_API_KEY"
-H "Content-Type: application/json"
-d '{"url":"https://example.com","user_agent":"Mozilla/5.0 (compatible; ExampleBot/1.0)"}'
--output screenshot.pngReplace the example key, URL, and User-Agent with values appropriate to your integration. Keep real API keys out of source control and published examples.
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ScreenshotCenter: use the documented query parameter
ScreenshotCenter’s endpoint reference lists user_agent as an optional query parameter. Use your HTTP client’s query-parameter encoding rather than concatenating an unescaped string: User-Agent values contain characters that need URL encoding. Its help article also shows user_agent in a JSON request object, so confirm which request format applies to the particular endpoint or client you are using. See the ScreenshotCenter documentation.
curl -G "YOUR_SCREENSHOTCENTER_ENDPOINT"
--data-urlencode "url=https://example.com"
--data-urlencode "user_agent=Mozilla/5.0 (compatible; ExampleBot/1.0)"Use the actual endpoint and authentication required by your ScreenshotCenter account; this pattern illustrates query encoding, not a substitute endpoint or credential format.
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shot-scraper: pass --user-agent
For the open-source command-line tool shot-scraper, the documentation identifies --user-agent as the User-Agent header option:
shot-scraper https://example.com --user-agent "Mozilla/5.0 (compatible; ExampleBot/1.0)"Refer to the shot-scraper documentation for installation, output options, and other CLI flags.
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Choose a value and verify the captured page
Use a truthful, purpose-specific string
Set a custom User-Agent for legitimate testing or compatibility work, such as checking how your own site responds to a client identifier. Do not use it to bypass a site’s access controls or terms. A User-Agent alone does not provide login credentials, cookies, or authorization.
Inspect the result, not just the API response
Some screenshot APIs can return an image of a login or error page rather than the page you intended to capture. Screenshot API documentation says a final page status of 401 or 403 indicates the result may be a login or error page. Check the final page status and image content, then address any authentication or cookie requirements. The User-Agent setting is documented configuration; it is not a guarantee that every provider applies it identically across redirects or subresource requests.
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Compare request details before adapting an example
When integrating a different provider, check its own documentation for these details rather than copying a field name from another API:
- Transport and parameter: GET query, POST JSON, or CLI flag, including exact spelling.
- Authentication: API key, bearer token, or another documented method.
- Related request controls: whether custom headers and cookies are supported, and how they interact with the User-Agent.
- Capture behavior: response format, viewport, and wait options relevant to the page you are testing.
These interfaces differ across the documented services; no single format should be treated as a universal screenshot API standard.
Troubleshooting
The target still shows the wrong content
Confirm the User-Agent parameter is spelled and placed exactly as the selected provider documents. Then inspect the captured image and final page status. If the page is a login or error screen, check whether the target requires authentication or cookies; changing the User-Agent by itself will not satisfy those requirements.
The API rejects the request or ignores the value
Check the endpoint’s required method and content type. A JSON property belongs in the request body when the provider documents a JSON body; a query parameter must be URL-encoded when sent in a URL. Do not assume a query parameter, body field, or command-line flag is interchangeable.
The custom value appears not to persist after navigation
Provider documentation describes how to configure the request, but does not establish identical propagation through redirects or every resource request. Test the relevant destination and ask the provider for details if the behavior matters to your integration.
Or skip the browser setup
ScreenshotNeo accepts a custom User-Agent and provides a one-request screenshot API. For example, this cURL call passes the User-Agent as a request parameter and saves the response:
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curl -G "https://api.screenshotneo.com/v1/shot" -d access_key=YOUR_API_KEY --data-urlencode url=https://stripe.com --data-urlencode user_agent="Mozilla/5.0 (compatible; ExampleBot/1.0)" -o shot.webpSee the ScreenshotNeo API documentation for authentication and request options. Before capture, it accepts cookie or consent banners like a visitor and removes more than 60 known consent platforms, newsletter popups, and chat widgets; each of those steps can be turned off. Bot checks, blank pages, timeouts, failed loads, and cache hits are not billed, and responses identify the page verdict and billing status in headers. Its MCP server offers take_screenshot, get_page_info, and capture_pdf for AI agents. The free plan includes 1,000 shots a month without a card; paid plans start at $5 for 3,000 shots. Sign up for ScreenshotNeo’s free plan.
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