By name: lex-sdk
description: >
Use this skill whenever code interacts with the @atproto/lex SDK family.
This family covers @atproto/lex and its companion packages:
@atproto/lex-client, @atproto/lex-data, @atproto/lex-json, and
@atproto/lex-schema (all re-exported by @atproto/lex), plus
@atproto/lex-cbor and @atproto/xrpc-server (related companion packages
that must be imported directly — they are NOT re-exported by @atproto/lex).
Trigger on ANY of the following (OR logic — match any one):
(1) XRPC calls with Client, xrpc, or xrpcSafe;
(2) defining XRPC server routes (createServer, server.add);
(3) validating lexicon-derived data ($build, $matches, $isTypeOf,
$parse, $safeParse, $validate);
(4) processing AT Protocol data: JSON ↔ Lex with lexParse / lexStringify /
jsonToLex / lexToJson, or CBOR via the separate @atproto/lex-cbor package;
(5) installing or building lexicons (lex install, lex build);
(6) working with branded strings (DidString, HandleString, AtUriString,
Cid, DatetimeString);
(7) handling blobs (BlobRef, TypedBlobRef, LegacyBlobRef);
(8) migrating a package from the legacy @atproto/api / @atproto/lexicon /
@atproto/xrpc / @atproto/lex-cli stack to @atproto/lex ("lexification").
(9) replacement for zod/joi/ajv validation libraries, in projects that already
require @atproto/lex.
When a task matches multiple triggers, consult all corresponding references
in the routing table below before responding.
disable-model-invocation: false
@atproto/lex SDK
@atproto/lex is the type-safe Lexicon SDK for AT Protocol. It generates
TypeScript schemas from Lexicon JSON, validates and builds data at runtime,
and provides an XRPC client + helpers for building services.
This skill is split into focused references. Read the ones relevant to the
current task — they are self-contained. If the task involves more than one
concern (e.g., migrating a client that also uses CBOR, or both server routes
and data validation), read all references whose Task column matches; when
in doubt, prefer reading more references over fewer. If a referenced .md
file is unavailable or cannot be read, state which file is missing and respond
using only the information in this SKILL.md and general AT Protocol knowledge,
noting the limitation explicitly.
When to read which reference
| Reference | Task |
|---|---|
| references/setup.md | Install lexicons, configure lex build, set up scripts/gitignore |
| references/schemas.md | Use generated schemas: $build, $matches, $isTypeOf, $parse, $safeParse, $validate, $type, $lxm, $Params, $Output. Create custom schemas with the l builder. |
| references/data-model.md | Work with AT Proto data: LexValue, Cid, BlobRef, JSON ↔ Lex, CBOR, datetime, branded strings (DidString, HandleString, AtUriString, …), graphemeLen/utf8Len |
| references/xrpc.md | Make low-level XRPC calls with xrpc() / xrpcSafe(), handle XrpcResponseError / XrpcInvalidResponseError / XrpcInternalError |
| references/client.md | Use the Client class: auth, call/create/get/put/delete/list/applyWrites, labelers, Actions, service proxy |
| references/server.md | Define XRPC server routes with @atproto/xrpc-server (createServer, server.add, handler shape) |
| references/lexification-server.md | Migrate service / server code from the legacy stack (old src/lexicon/, ids.*, Server from generated code, server.app.bsky.…() chains) |
| references/lexification-client.md | Migrate client / consumer code from the legacy stack (AtpAgent → Client, .data → .body, XRPCError → XrpcError, jsonStringToLex → lexParse, etc.) |
Top-level package layout
The @atproto/lex SDK family is split into two groups:
- Re-exported sub-packages:
@atproto/lex-client,@atproto/lex-schema,@atproto/lex-data,@atproto/lex-json. Importing from either@atproto/lexor the sub-package path works. - Companion packages (NOT re-exported):
@atproto/lex-cborand@atproto/xrpc-server. These are part of the SDK family and trigger this skill, but they must be imported directly from their own package paths — never from@atproto/lex.
| Sub-package | Provides |
|---|---|
@atproto/lex-client |
Client, xrpc, xrpcSafe, XrpcResponseError, XrpcInvalidResponseError, XrpcInternalError, XrpcResponseValidationError |
@atproto/lex-schema |
The l schema-builder namespace, Schema types, validation primitives |
@atproto/lex-data |
LexValue, LexMap, Cid, parseCid, BlobRef, TypedBlobRef, LegacyBlobRef, branded strings (DidString, HandleString, AtUriString, DatetimeString, …), graphemeLen, utf8Len, isLanguageString |
@atproto/lex-json |
lexParse, lexStringify, jsonToLex, lexToJson, parseLexLink, encodeLexLink, parseLexBytes, encodeLexBytes |
@atproto/lex-cbor |
CBOR encode / decode (separate package, not re-exported by @atproto/lex) |
@atproto/xrpc-server |
createServer, Server type, Headers (used to define server routes — not re-exported by @atproto/lex) |
Generated code conventions
- Lexicon JSON lives in
./lexicons/, manifest inlexicons.json(ormanifest.json— both are committed). - Generated TS lives in
./src/lexicons/(plural — gitignored, regenerated bylex build). - Import the namespace tree from the index:
import { app, com, chat } from './lexicons/index.js'. - Schemas are accessed by NSID dot-path:
app.bsky.feed.post,com.atproto.repo.getRecord,app.bsky.feed.defs.postView.
Related skills
When writing or migrating tests for code that uses @atproto/lex, also see the testing skill — it covers runner choice (vitest vs jest), test file location, and tsconfig setup.