resolving-domains

name	resolving-domains
description	ENS and Web3 identity resolution for XMTP agents. Use when resolving domain names, extracting mentions, or fetching Farcaster profiles. Triggers on ENS resolution, Farcaster lookup, or mention extraction.
license	MIT
metadata	{"author":"xmtp","version":"1.0.0"}

XMTP domain resolver

Resolve Web3 identities including ENS, Farcaster, Basenames, and Lens Protocol.

When to apply

Reference these guidelines when:

• Resolving ENS names to addresses
• Extracting @mentions from messages
• Fetching Farcaster profiles
• Working with shortened addresses in groups

Rule categories by priority

Priority	Category	Impact	Prefix
1	Resolve	HIGH	resolve-
2	Extract	HIGH	extract-
3	Profiles	MEDIUM	profiles-

Quick reference

Resolve (HIGH)

• resolve-address - Resolve domain names to addresses
• resolve-mentions - Resolve all mentions in a message

Extract (HIGH)

• extract-mentions - Extract @mentions from text

Profiles (MEDIUM)

• profiles-farcaster - Fetch Farcaster profile data

Supported platforms

• ENS - vitalik.eth
• Farcaster - dwr.eth, username.farcaster.eth
• Basenames - tony.base.eth
• Lens Protocol - stani.lens

Quick start

import { createNameResolver } from "@xmtp/agent-sdk/user";

// Resolve a single name using the SDK resolver
const resolver = createNameResolver(process.env.WEB3_BIO_API_KEY || "");
const address = await resolver("vitalik.eth");

// Resolve all mentions in a message
const resolved = await resolveMentionsInMessage(
  ctx.message.content,
  await ctx.conversation.members()
);
// Returns: { "bankr.eth": "0x...", "@fabri": "0x..." }

// Get Farcaster profile via web3.bio API
const profile = await fetchFarcasterProfile("dwr.eth");
console.log(profile.username, profile.fid);

Implementation snippets

Extract mentions from text:

const extractMentions = (message: string): string[] => {
  const mentions: string[] = [];
  
  // Full addresses
  const addresses = message.match(/(0x[a-fA-F0-9]{40})\b/g);
  if (addresses) mentions.push(...addresses);
  
  // @mentions and domains
  const atMentions = message.match(/@(?!0x)([\w.-]+\.eth|[\w.-]+)/g);
  if (atMentions) mentions.push(...atMentions.map(m => m.slice(1)));
  
  // Standalone domains
  const domains = message.match(/\b([\w-]+(?:\.[\w-]+)*\.eth)\b/g);
  if (domains) mentions.push(...domains);
  
  return [...new Set(mentions)];
};

Resolve mentions in message:

import { createNameResolver } from "@xmtp/agent-sdk/user";

const resolveMentionsInMessage = async (
  message: string, members?: GroupMember[]
): Promise<Record<string, string | null>> => {
  const resolver = createNameResolver(process.env.WEB3_BIO_API_KEY || "");
  const mentions = extractMentions(message);
  const results: Record<string, string | null> = {};
  
  await Promise.all(mentions.map(async (mention) => {
    if (mention.match(/^0x[a-fA-F0-9]{40}$/)) {
      results[mention] = mention;
    } else {
      const name = mention.includes(".") ? mention : `${mention}.farcaster.eth`;
      results[mention] = await resolver(name).catch(() => null);
    }
  }));
  return results;
};

Fetch Farcaster profile:

const fetchFarcasterProfile = async (name: string) => {
  const response = await fetch(`https://api.web3.bio/profile/${encodeURIComponent(name)}`);
  if (!response.ok) return { address: null, username: null, fid: null };
  const data = await response.json();
  const profile = data?.find((p: any) => p.platform === "farcaster");
  return {
    address: profile?.address,
    username: profile?.displayName,
    fid: profile?.social?.uid?.toString(),
  };
};

How to use

Read individual rule files for detailed explanations:

rules/resolve-address.md
rules/extract-mentions.md
rules/profiles-farcaster.md