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To approximate a PDF made by wkhtmltopdf, serve the HTML locally, match the conversion’s viewport width and page settings in your browser, and use the same media mode and content-ready state. This is only a preview: wkhtmltopdf uses Qt WebKit, so current Chrome or Chromium can lay out some CSS differently. Verify the final result with the same wkhtmltopdf binary and options used to make the PDF.
Why a browser preview may differ from wkhtmltopdf
wkhtmltopdf is an open-source command-line tool that converts HTML to PDF using Qt WebKit. That is not the Blink engine used by current Chrome and Chromium. A Chrome preview can help you tune dimensions, wrapping, and content readiness, but it cannot guarantee identical rendering when the engines interpret CSS differently.
Compatibility documentation for wkhtmltopdf 0.12.6 warns that its Qt WebKit build does not support flexbox, grid, and many newer CSS features. Treat that as a warning for that implementation and version, not as a guarantee about every binary: check the version and build installed in your environment. If the document relies on modern layout features, use the actual converter to determine what the PDF will do.
Set up a browser preview that is useful
1. Serve the HTML over HTTP
Open the page through a local web server, such as an http://localhost origin, rather than relying on a file URL. This gives relative stylesheets, fonts, images, and scripts an HTTP origin similar to the one used in conversion, and makes missing assets easier to spot in the browser’s developer tools.
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Use the same source files and asset paths as the conversion. If wkhtmltopdf receives a URL, preview that URL or an equivalent local copy. If it receives a local file, make sure its relative resources resolve the same way. A preview with missing fonts or images is not a meaningful comparison.
2. Match the viewport width
In browser developer tools, enable device emulation or set a custom viewport whose width matches the width passed to wkhtmltopdf with --viewport-size. The corresponding library setting is named screenWidth. This width affects line lengths, wrapping, and responsive breakpoints; it is distinct from the physical width of the paper.
Do not assume the paper width alone determines the layout viewport. Use the exact viewport setting from the production command, if one is present. If the command does not specify it, record that fact and compare the browser preview against the converter’s actual output rather than guessing at an undocumented default.
3. Match paper, orientation, and margins
wkhtmltopdf documents A4 as its default paper size, unless another size is selected. Match the paper size and orientation used by the command, as well as all four margins. Those settings affect available printable width and pagination. They do not replace the viewport setting.
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In Chrome’s print preview, choose the same paper size, orientation, and margins when inspecting page breaks. Browser print controls and wkhtmltopdf are not the same rendering implementation, so this comparison remains approximate. Keep a note of the exact command-line values or configuration used; a visually similar browser dialog is not proof that the PDF settings match.
4. Choose the same media mode
wkhtmltopdf uses screen media by default. It switches to print media only when the conversion includes --print-media-type. Therefore, a normal screen preview is the appropriate starting point for the default command. If the command uses --print-media-type, emulate print media in browser developer tools or inspect the page in print preview.
The official usage documentation describes --print-media-type as using print media type instead of screen. Check the actual command rather than assuming that a PDF necessarily means print CSS is active.
5. Wait for the same page state
A page with asynchronous content can change after its initial load. wkhtmltopdf offers --javascript-delay, --run-script, and --window-status to influence when it captures. In the browser, wait for the same meaningful condition: for example, the chart has rendered, the data request has completed, or the application has set its ready status. A fixed delay can help reproduce a known command, but waiting for a specific ready state is generally easier to reason about than comparing two captures taken at arbitrary times.
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6. Inspect the details that alter the PDF
- Compare line wrapping and text width at the target viewport.
- Check horizontal overflow and content clipped at the page edges.
- Confirm fonts have loaded and images use the expected dimensions.
- Inspect page breaks in the browser print preview, then confirm them with wkhtmltopdf.
- Check whether the command enables or disables smart shrinking. Its intelligent shrinking can change the pixel-to-DPI ratio, so reproduce that setting when diagnosing scale differences.
What controls to check in the wkhtmltopdf command
| Setting | Why it matters | What to match |
|---|---|---|
--viewport-size / screenWidth |
Changes layout width, line wrapping, and responsive behavior. | Use the same viewport width in the browser. |
--print-media-type |
Selects print CSS instead of the default screen media. | Use screen unless the command opts into print; emulate the selected mode. |
| Paper size, orientation, and margins | Change the printable area and where page cuts fall. A4 is the documented default paper size when not overridden. | Match the command’s selected paper dimensions, orientation, and margins. |
--javascript-delay, --run-script, --window-status |
Affect when dynamic content is ready for capture. | Wait for the equivalent content or application-ready condition in the browser. |
| Smart shrinking | Can change the pixel-to-DPI ratio and perceived scale. | Reproduce the command’s enabled or disabled state during diagnosis. |
Understand page breaks and CSS limits
wkhtmltopdf lays out a long WebKit page and then cuts it into paper pages. Page-break positions therefore depend on the layout width, content height, paper dimensions, margins, and scaling. A paragraph that wraps to one extra line can shift content below it and move later breaks, so investigate the first point where the browser and PDF diverge rather than adjusting every later page independently.
Prefer CSS and layouts supported by the Qt WebKit build you actually run. If a flexbox or grid layout differs in the PDF, a contemporary browser preview cannot repair the underlying engine mismatch. A simpler layout supported by the target build may be more predictable. Keep the production binary version consistent across development and deployment where reproducibility matters.
Verify with the actual converter
After the browser preview looks right, render the HTML with the exact wkhtmltopdf binary, options, assets, and environment used in production. The PDF from that run is the acceptance check. If production runs a different binary or command, reproduce that environment before relying on a local result.
For a fair comparison, keep the HTML and data fixed, then change one setting at a time: viewport, media mode, page geometry, timing, or shrinking. This makes it easier to identify whether a mismatch comes from layout, pagination, or content that was not ready at capture time.
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Troubleshooting mismatches
Text wraps differently
First compare viewport widths and loaded fonts. Then check whether the browser and wkhtmltopdf are using the same media mode. If those match, suspect a rendering-engine difference, especially when the page uses CSS newer than the Qt WebKit build supports.
The PDF is scaled or content is clipped
Compare paper size, orientation, margins, viewport, and smart-shrinking state. A narrower printable area or a different shrink ratio can alter apparent scale even when the CSS is unchanged. Check for horizontal overflow at the converter’s viewport width.
Page breaks shift farther down the document
Find the earliest divergence in the text or element heights. A small difference in font metrics, wrapping, image size, or loaded content can accumulate as the long page is cut into pages. Confirm page geometry and dynamic content readiness before making page-break CSS changes.
Charts, images, or fonts are missing
Verify that the resources load from the same origin and paths, and wait for the same readiness condition. Use browser developer tools to inspect failed requests and font loading. If the browser succeeds but the converter does not, check the converter’s own output and environment; the browser is not evidence that every dependency was available to wkhtmltopdf.
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Chrome looks correct but the PDF layout is broken
Check for flexbox, grid, or other unsupported CSS in the target Qt WebKit implementation. Reproduce with the installed wkhtmltopdf binary, then simplify or adapt the layout for that engine if needed. Do not treat a Chrome-only fix as proof the converter will render it correctly.
Or skip the browser setup
If the goal is a screenshot of a live web page rather than a faithful preview of wkhtmltopdf’s Qt WebKit PDF output, ScreenshotNeo can capture a URL with a single request. It is a screenshot API and MCP server, not a replacement for validating a wkhtmltopdf PDF; the engines and output workflows differ. See the ScreenshotNeo API documentation for request options.
Example cURL request:
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Frequently Asked Questions
Can Chrome produce an identical preview of a wkhtmltopdf PDF?
Not reliably: Chrome uses Blink while wkhtmltopdf uses Qt WebKit. Match the settings for a useful approximation, then verify with the actual converter.
Does wkhtmltopdf use print CSS by default?
No. It uses screen media by default; --print-media-type opts into print media.
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