This package provides a WebFinger client implementation for looking up ActivityPub actors and other resources in the fediverse. It is part of the Fedify framework but can be used independently.

• WebFinger resource lookup (RFC 7033)
• Support for acct: URI scheme
• Automatic HTTPS URL construction
• Configurable redirect handling
• OpenTelemetry integration for tracing
• Private IP address validation for security

deno add jsr:@fedify/webfinger  # Deno
npm add @fedify/webfinger       # npm
pnpm add @fedify/webfinger      # pnpm
yarn add @fedify/webfinger      # Yarn
bun add @fedify/webfinger       # Bun

You can look up a WebFinger resource using the lookupWebFinger() function:

import { lookupWebFinger } from "@fedify/webfinger";

// Look up by acct: URI
const result = await lookupWebFinger("acct:alice@example.com");

// Look up by URL
const result2 = await lookupWebFinger("https://example.com/users/alice");

The result is a ResourceDescriptor object containing the subject, aliases, properties, and links:

import { lookupWebFinger } from "@fedify/webfinger";

const result = await lookupWebFinger("acct:alice@example.com");
if (result != null) {
  console.log("Subject:", result.subject);
  console.log("Aliases:", result.aliases);

  // Find the ActivityPub actor URL
  const actorLink = result.links?.find(
    (link) => link.rel === "self" && link.type === "application/activity+json"
  );
  if (actorLink?.href != null) {
    console.log("Actor URL:", actorLink.href);
  }
}

The lookupWebFinger() function accepts various options:

import { lookupWebFinger } from "@fedify/webfinger";

const result = await lookupWebFinger("acct:alice@example.com", {
  // Custom User-Agent header
  userAgent: "MyApp/1.0",

  // Maximum redirects to follow (default: 5)
  maxRedirection: 3,

  // AbortSignal for cancellation
  signal: AbortSignal.timeout(5000),
});

• lookupWebFinger(resource, options?): Looks up a WebFinger resource and returns a ResourceDescriptor or null if not found.

• ResourceDescriptor: Describes a WebFinger resource with subject, aliases, properties, and links.
• Link: Represents a link in a WebFinger response with relation type, media type, href, titles, and properties.
• LookupWebFingerOptions: Options for the lookupWebFinger() function.

For comprehensive documentation, please refer to:

• WebFinger documentation
• API reference

• @fedify/fedify: The main Fedify framework
• @fedify/vocab: Activity Vocabulary library

MIT License