LexDNS

LexDNS resolves AT Protocol Lexicon schemas from NSIDs.

It turns names like app.bsky.feed.post into the DNS location that advertises the schema publisher, follows the publisher’s DID document to its PDS to obtain the matching com.atproto.lexicon.schema record.

Why I Built This

AT Protocol Lexicons are meant to be named, discoverable schemas.

I wanted a small resolver to add to Ibex that made that discovery path easy so I wouldn’t need to embed generated schema packages into every project.

Features

• REST endpoint for resolving an NSID to source metadata and the Lexicon document
• DNS-over-HTTPS TXT lookup for _lexicon.<authority-domain> records
  • did=... TXT record discovery for Lexicon publishers
  • DID document resolution for did:plc and did:web
  • PDS lookup through the #atproto_pds service
  • Schema fetch through com.atproto.repo.getRecord
• Response links for the API result and original at:// source record
• KV-backed cache with configurable TTL
• Small web UI for trying published Lexicons interactively
• CORS support for browser clients

Architecture

LexDNS runs as a Cloudflare Worker using Hono for routing & templating (JSX).

The resolver:

1. validates the NSID
2. converts its authority into the _lexicon DNS name
3. reads TXT records through DNS over HTTPS
4. resolves the publisher DID
5. fetches the schema record from the publisher’s PDS.

Successful results are stored in Workers KV so repeated lookups stay cheap.

Status

LexDNS is live.