Getting started

Mermaider renders Mermaid diagram syntax to sanitized SVG in pure .NET — no JavaScript runtime, no headless browser, no subprocess.

dotnet add package Mermaider

Targets net10.0. No transitive native or JavaScript dependencies.

using Mermaider;

string svg = MermaidRenderer.RenderSvg("""
    flowchart LR
      A[Parse] --> B[Layout] --> C[Render SVG]
""");

// svg is a complete, sanitized SVG string — embed it directly in HTML
Response.Write(svg);

RenderSvg returns a self-contained SVG string. Write it into your HTML response, save it to disk, or pipe it anywhere — no further processing needed.

// Write SVG bytes directly to an HTTP response stream
await MermaidRenderer.RenderSvgAsync(diagram, Response.Body, cancellationToken: ct);

// Or to a PipeWriter for zero-copy scenarios
await MermaidRenderer.RenderSvgAsync(diagram, pipeWriter, cancellationToken: ct);

The CancellationToken is honored throughout the full parse → layout → render pipeline, not only on the final write.

Pass a RenderOptions record to control colors, fonts, layout, and security behavior:

var options = new RenderOptions
{
    Bg = "#0D1117",
    Fg = "#E6EDF3",
    Accent = "#58A6FF",
    Font = "Inter",
    Style = DiagramStyle.Quiet,
    Transparent = true,
    Strict = new StrictStylingOptions()
};

string svg = MermaidRenderer.RenderSvg(diagram, options);

1. or Blueprint / Tonal

See Theming for the colour tokens, the built-in themes, the style presets and the colour roles, and Security for strict mode and sanitization options.

RenderAscii draws flowcharts, state diagrams and XY charts as text, for terminals and logs:

string text = MermaidRenderer.RenderAscii(diagram, new AsciiOptions { Width = 80 });

Set AsciiOptions.Ascii = true for plain ASCII instead of box-drawing characters. Other diagram types throw NotSupportedException.

The Mermaider.Cli tool renders a file or standard input to SVG:

dotnet tool install -g Mermaider.Cli

mermaid diagram.mmd -o diagram.svg
mermaid diagram.mmd -t github-dark --style blueprint -o diagram.svg
echo 'graph TD; A-->B' | mermaid > diagram.svg

MermaidResourceLimitException is a subtype of MermaidParseException — existing catch (MermaidParseException) blocks automatically cover limit violations.

MermaidRenderer is a static class. RenderSvg is thread-safe — call it concurrently from as many threads as you like. Internal ObjectPool<StringBuilder> instances are shared across calls.