Troubleshooting & Best Practices

Even with a solid installation, VitePress documentation sites can run into Mermaid rendering quirks once they hit production. This checklist helps you diagnose the most common issues quickly.

1. Installation or Update Issues

Errors can sometimes occur after installing the package or updating to a new version. To resolve these, try clearing VitePress's cache and build artifacts. Deleting the .vitepress/cache and dist (or your build output) folders and then restarting the development server often fixes unexpected behavior caused by stale dependencies.

2. Diagrams fail to appear

• Confirm Mermaid code fences are marked with ```mermaid and not ```mermaind (typos block detection).
• Run npm run docs:dev and inspect the console for hydration errors before deploying. Missing dependencies often log as createMermaidRenderer is not defined or window is not defined.

3. Toolbar missing buttons

• Check setToolbar() configuration; the renderer merges deeply, so a misconfigured nested object can drop buttons for all breakpoints.
• When you need a lean toolbar per diagram, call mermaidRenderer.setToolbar() immediately after createMermaidRenderer() and before the first render.
• Mobile toolbars hide by default in narrow viewports—but they can reappear if you stretch the window. Use positions to keep buttons pinned in the same corner across breakpoints.

4. Dark mode renders incorrectly

• Confirm you watch useData().isDark and re-render when it changes. Without this hook, Mermaid sticks to the theme active during the initial load.
• Add mermaidRenderer.setConfig({ theme: isDark.value ? "dark" : "default" }) inside the watcher to keep CSS variables in sync.

5. Build-time SVG breaks

• Clean .vitepress/cache before vitepress build when you change Mermaid dependencies; stale cache entries lock in old versions of the renderer.

6. Accessibility checks

• Screen readers rely on showLanguageLabel to announce that the container is a Mermaid diagram. Keep it enabled or add descriptive labels manually.
• Provide alt text equivalents in surrounding prose when diagrams convey critical information.

7. Best practices recap

• Cache the renderer instance and reuse it across renders to avoid unnecessary initialization.

By following this checklist, your interactive Mermaid diagrams remain resilient, performant, and aligned with search engine expectations.