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Link safety

Sanitization decides which HTML can exist. Link safety separately decides where anchors and images can point. Use both for untrusted model output.

Defaults​

HyperMarkdown permits http, https, mailto, and tel URLs by default. Links open in a new tab with rel="noreferrer". Images load lazily, decode asynchronously, and use referrerPolicy="no-referrer".

Data images are permitted by default. Narrow that policy when model output must not embed arbitrary image data.

Restrict destinations​

<HyperMarkdown
  md={markdown}
  linkSafety={{
    allowedProtocols: ["https"],
    allowedLinkPrefixes: ["https://docs.example.com/"],
    allowedImagePrefixes: ["https://images.example.com/"],
    allowDataImages: false,
  }}
/>

Use allowedLinkPrefixes: ["*"] or allowedImagePrefixes: ["*"] to allow any destination that already passed the protocol check.

Footnotes are local​

Footnote references and back-references are recognized separately. They update the page hash rather than opening a new tab, preserving normal footnote navigation.

Defense in depth​

URL filtering cannot control what an allowed remote server returns. Combine the renderer policy with a Content Security Policy and an image proxy when the application has a strict trust boundary.