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First identify the language your diagram code uses: PlantUML and Mermaid need different renderers. For PlantUML, run the PlantUML command-line tool to create a PNG by default, or select SVG; for Mermaid, use Mermaid CLI to export SVG, PNG, or PDF. If you only have a diagram page open in a browser, you can capture that page as an image, but a website screenshot API does not convert raw UML code into a diagram.
Identify the diagram language before converting it
Look at the source file and its syntax before choosing a tool. PlantUML and Mermaid are separate diagram languages: Mermaid CLI accepts Mermaid definitions, not arbitrary PlantUML or other UML source. If the file came from a particular editor or project, check which syntax it exports and choose a renderer for that language.
- For PlantUML source, use PlantUML’s command-line renderer or server.
- For Mermaid source, use Mermaid CLI.
- If the source uses another language, use a renderer that explicitly supports it; the workflows below do not establish support for every UML dialect.
Convert PlantUML code with the command line
With Java and the PlantUML JAR or packaged build available, run the command from the directory containing the diagram file:
java -jar plantuml.jar diagram.pumlPlantUML checks for diagram markers and creates a PNG by default. The command-line tool can also process multiple input files, such as:
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java -jar plantuml.jar file1 file2 file3To create an SVG instead, select the format explicitly:
java -jar plantuml.jar --svg diagram.pumlThe documented command-line options also include PDF and other output formats. Consult the PlantUML command-line documentation for the exact option supported by the build you are using. Installation differs depending on how you obtained PlantUML, so do not assume that the JAR is already in your working directory or that a particular operating system’s package manager is required.
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Render a directory or multiple diagrams
PlantUML can process multiple source files and directories. Run it with the relevant files or directory as input, then check the output location for the generated images. For project-wide rendering, keep the source and generated files organized so that repeated runs do not overwrite or mix unrelated diagrams.
Control source metadata in PNG files
PlantUML PNG output can contain encoded source metadata. Use -nometadata when you do not want that metadata embedded. The -metadata option can extract metadata from a local PNG.
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Render PlantUML through PlantUML Server
If you do not want to set up the local command-line tool, PlantUML Server provides routes that return an image from encoded PlantUML source. The documented route patterns are /plantuml/png/ENCODED for PNG and /plantuml/svg/ENCODED for SVG. Encode the diagram source as required by the server before placing it in the route; the word ENCODED represents the encoded source, not literal UML text.
SVG is not available for every diagram type. If an SVG request cannot render a particular diagram, try PNG instead; ditaa is one documented example that is available only as PNG. Organizations can also install PlantUML Server on their own Java web server. The current server documentation specifies Tomcat 10 because of the javax.*-to-jakarta.* transition; check the documentation for the version you intend to deploy.
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Convert Mermaid code with Mermaid CLI
For a Mermaid definition file, Mermaid CLI can generate SVG, PNG, or PDF. With the CLI installed, save the definition as input.mmd and run:
mmdc -i input.mmd -o output.svgChange the output extension to .png or .pdf for those formats. The documented installation methods include npm and Docker or Podman. This command is for Mermaid source; it is not a general converter for PlantUML files.
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Choose PNG, SVG, or PDF
| Format | Best fit | Important consideration |
|---|---|---|
| PNG | Sharing an image with broad viewer compatibility | PlantUML uses PNG by default. Some PlantUML diagram types may not support SVG, so PNG can be the fallback. |
| SVG | Web pages and documentation where vector scaling is useful | PlantUML and Mermaid CLI document SVG export, but support depends on the renderer and diagram type. |
| Documents and print workflows | Both PlantUML CLI and Mermaid CLI document PDF output. |
Use the format option supported by your renderer rather than assuming that changing a filename extension alone converts the content.
Troubleshoot a failed conversion
- The source is not recognized: Verify whether it is PlantUML, Mermaid, or another diagram language, then use a renderer for that syntax. Mermaid CLI does not convert arbitrary UML source.
- No image appears where expected: PlantUML writes a PNG by default. Check the command’s working directory and the source file path, and confirm that you ran the command against the intended file.
- SVG output fails: The diagram type may not support SVG. Try PNG, which PlantUML uses by default.
- The image is not the requested format: Choose the format using the renderer’s documented option or output extension; do not treat renaming a file as conversion.
- The server route does not work with raw source: The PlantUML Server route expects encoded source in the URL path. Encode the diagram before constructing the request.
Syntax errors can also prevent rendering. Check the diagram definition and the renderer’s output for the specific issue; the documented format and interface references do not establish one universal error message or fix for every failure.
Or skip the browser setup
If your UML diagram is already rendered on a web page, ScreenshotNeo can capture that page; it does not take raw PlantUML or Mermaid code as input or render it into a diagram. For example, point the request at a browser-accessible page containing the rendered diagram. Replace the sample page URL and API key with your own values. See the ScreenshotNeo documentation for request options.
Quick Recap
curl -G "https://api.screenshotneo.com/v1/shot" -d access_key=YOUR_API_KEY --data-urlencode url=https://your-site.example/diagram-page -o shot.webpScreenshotNeo accepts cookie or consent banners before capture and removes more than 60 known consent platforms, newsletter popups, and chat widgets; those steps can be turned off. Bot checks, blank pages, timeouts, failed loads, and cache hits are not billed, and response headers report the page verdict and billing status. Its MCP server provides take_screenshot, get_page_info, and capture_pdf tools for AI agents. The Free plan includes 1,000 shots per month with no card; paid plans start at $5 for 3,000 shots. Learn about ScreenshotNeo or sign up free for 1,000 screenshots a month with no card.
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