Use the renderer that understands your diagram’s source language: Mermaid code goes to Mermaid CLI (mmdc), PlantUML source to PlantUML’s Java command line, and DOT source to Graphviz’s dot command. Choose SVG when you need crisp scaling, PNG when you need a broadly compatible image, or PDF for a document or report.
Identify the diagram language first
Diagram source is not interchangeable: a renderer needs to understand the syntax in the file. Check the first few lines, the file extension, or the editor where the diagram was created. Common clues are Mermaid declarations such as flowchart or sequenceDiagram, PlantUML’s @startuml and @enduml markers, and DOT statements such as digraph or graph.
| Source | Renderer | Typical command | Good first format |
|---|---|---|---|
| Mermaid definition | Mermaid CLI | mmdc -i input.mmd -o output.svg |
SVG or PNG |
| PlantUML source | PlantUML Java archive | java -jar plantuml.jar -t svg diagram.puml |
PNG by default; SVG or PDF when needed |
| DOT source | Graphviz dot |
dot -Tsvg input.dot > output.svg |
SVG or PNG |
| Mermaid diagram in a hosted editor | Mermaid Chart | Use the editor’s export controls | PNG, SVG, or PDF |
If you only have an image or a webpage displaying a diagram, these source-code renderers are not the first step: they render diagram definitions, not arbitrary screenshots. For code, match the syntax to a renderer before changing file extensions; renaming a DOT file to .mmd, for example, does not convert its contents.
Choose an output format
SVG for scaling and reuse
SVG is a vector format and can scale without the pixelation associated with enlarging a raster image. It is a strong choice for web pages, documentation, and print workflows that accept SVG. Mermaid CLI and PlantUML can produce it, and Graphviz selects it with -Tsvg.
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PNG for broad compatibility
PNG is a practical choice when you need a conventional image for a presentation, document, or application that does not handle SVG. Mermaid CLI can write PNG by using a .png output filename; PlantUML uses PNG by default; Graphviz selects it with -Tpng. PNG is raster-based, so choose adequate dimensions if the image will be enlarged.
PDF for reports and handoff
Use PDF when the deliverable is a report or a document that should preserve a page-oriented layout. Mermaid CLI and PlantUML support PDF output. Mermaid Chart’s export guide also describes PDF as an option for reports. Check the result at the intended page size: a diagram that is legible on screen can become too small if it is placed on a page without adjusting its layout.
Convert Mermaid code with Mermaid CLI
Mermaid CLI takes a Mermaid definition file and generates SVG, PNG, or PDF. Install the CLI with npm, then pass the source file with -i and the destination filename with -o.
-
Install the package:
npm install -g @mermaid-js/mermaid-cli.Special offer. See more information about Outbyte and uninstall instructions. Please review EULA and Privacy policy. -
Save the Mermaid definition as
input.mmd. -
Render to SVG:
mmdc -i input.mmd -o output.svg. -
For PNG instead, run:
mmdc -i input.mmd -o output.png.
For example, if flow.mmd contains a valid Mermaid flowchart, mmdc -i flow.mmd -o flow.svg creates an SVG output. The output extension is the key format choice in these examples. The CLI also supports themes and transparent PNG backgrounds; for example, mmdc -i input.mmd -o output.png -t dark -b transparent selects the dark theme and a transparent background.
Export PlantUML as an image
PlantUML runs from its Java archive. If you have a local plantuml.jar and Java available, pass one or more source files to the archive. PNG is the default output; add -t to select SVG or PDF.
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Render a PlantUML source file with the default PNG output:
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Choose SVG explicitly:
java -jar plantuml.jar -t svg diagram.puml. -
Choose PDF for a report workflow:
java -jar plantuml.jar -t pdf diagram.puml.
The command-line tool can process directories and common PlantUML source extensions, so it also fits batch rendering. Start with one file and confirm its output before using a directory-wide command; that makes it easier to spot a malformed source file or an unexpected output location.
Turn DOT source into SVG or PNG with Graphviz
Graphviz’s dot command reads DOT files or standard input. The -T flag selects the output format, and shell redirection writes the rendered bytes to a file.
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Render a file as SVG:
dot -Tsvg input.dot > output.svg. -
Render the same source as PNG:
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Or pipe DOT text directly to Graphviz:
echo 'digraph { a -> b }' | dot -Tsvg > output.svg.
In the final example, the shell’s > writes the output file; it is not part of DOT syntax. Use single quotes around the inline definition so the shell passes it as one string. For larger diagrams or scripts, a source file is easier to edit and review.
Use a hosted Mermaid editor if you do not want a local CLI
Mermaid Chart provides a browser-based workflow for exporting a finished Mermaid diagram. Use its export controls to choose PNG, SVG, or PDF. This is convenient when you want to edit or export in a hosted editor rather than install and run a local renderer. It is a digital service, not a physical product.
For repeatable builds, the command-line route is usually easier to incorporate into a shell script or documentation build: Mermaid CLI, PlantUML, and Graphviz all support command-line rendering. For an occasional export where a hosted editor is preferable, Mermaid Chart offers the browser workflow. Choose based on how the diagram is authored and where the result needs to go, rather than on format alone.
Automate repeatable exports
Once the source file renders correctly, the same command can be used in a script or CI job. Keep the source and output names explicit, and choose the format in the command rather than relying on someone to export manually from an editor. Mermaid CLI’s input and output flags, PlantUML’s Java invocation, and Graphviz’s format flag make these workflows suitable for repeatable documentation builds.
-
Keep the source definition in the project so an image can be regenerated after edits.
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Render to the format the consuming tool actually supports; SVG may be a good default for web use, while PNG may be simpler for software that expects raster images.
-
When a build fails, inspect the renderer’s diagnostic output and the source syntax before treating the result as an image-format problem.
Troubleshoot common conversion problems
The command is not found
If the shell reports that mmdc or dot is not found, the relevant CLI may not be installed or may not be on the shell’s executable path. For PlantUML, check that the Java command works and that the path to plantuml.jar is correct. Run the command from the directory containing the source file, or provide its full path.
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Confirm that the source language matches the renderer: Mermaid definitions need Mermaid CLI, PlantUML syntax needs PlantUML, and DOT syntax needs Graphviz. Then inspect the reported line or nearby delimiters and punctuation. A file extension can help you identify a file, but it does not change the language the contents are written in.
The output is not the format you expected
Check the output name and format selector. Mermaid CLI’s examples use the output extension, PlantUML defaults to PNG unless you pass -t, and Graphviz uses -Tsvg or -Tpng. Do not assume all three tools choose formats the same way.
The result looks jagged or will not open
If you enlarged a PNG, try SVG where the destination supports it, or render a PNG at dimensions appropriate for its final placement. If a viewer does not accept SVG, use PNG or PDF as appropriate. When a file cannot be opened, verify that the command completed successfully and that the output file contains the rendered result rather than an error message redirected into it.
The diagram appears too small in a PDF or presentation
Check the intended page or slide size and the diagram’s layout before exporting again. Changing the format does not automatically make a crowded diagram readable. Use a vector output for scaling when supported, and inspect the actual placement in the destination document.
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Or skip the browser setup
ScreenshotNeo is for capturing a rendered webpage, not for converting Mermaid, PlantUML, or DOT source code directly. If your diagram is already displayed on a webpage and you need a screenshot of that page, its website screenshot API can return an image or PDF with one GET request. See the ScreenshotNeo API documentation.
curl -G "https://api.screenshotneo.com/v1/shot" -d access_key=YOUR_API_KEY --data-urlencode url=https://stripe.com -o shot.webpWith a URL in place, the same call in Python is:
import requests
r = requests.get("https://api.screenshotneo.com/v1/shot", params={"access_key": "YOUR_API_KEY", "url": "https://stripe.com"}, timeout=90)
open("shot.webp", "wb").write(r.content)Or in Node.js:
const q = new URLSearchParams({ access_key: 'YOUR_API_KEY', url: 'https://stripe.com' });
const res = await fetch(`https://api.screenshotneo.com/v1/shot?${q}`);-
Cookie and consent banners are accepted like a visitor and removed, along with supported newsletter popups and chat widgets; each cleanup step can be turned off.
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Bot checks or CAPTCHAs, blank pages, timeouts, failed loads, and cache hits are not billed. Response headers identify the page verdict and billing status.
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Cost and reliability considerations
Local command-line rendering puts the conversion in your own environment and can be repeated without a browser-based export step. It also means your build depends on having the matching renderer available: Mermaid CLI for Mermaid, Java and PlantUML for PlantUML, or Graphviz for DOT. If you choose a hosted editor, you trade local setup for a browser-based service workflow. The supplied tools support repeatable rendering, but the source material does not establish comparative rendering speed or reliability figures, so choose using your syntax, output needs, and environment rather than an assumed performance ranking.
For ScreenshotNeo, treat the API as a webpage-capture step only after the diagram has been rendered and published somewhere accessible by URL. It is not a substitute for the syntax-specific commands above. Its billing behavior distinguishes billable clean captures from the non-billed conditions listed in the response, which can help when automating screenshot capture of finished diagrams.
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Can I convert Mermaid, PlantUML, and DOT source with the same command?
No. Each renderer understands its own diagram language: use Mermaid CLI, PlantUML’s Java command line, or Graphviz’s dot for the matching source.
Does ScreenshotNeo turn Mermaid code directly into an image?
No. ScreenshotNeo captures webpages by URL. Render the diagram with its language-specific tool first; ScreenshotNeo can capture it if it is displayed on an accessible webpage.
Quick Recap
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