diff --git a/README.md b/README.md
index 5660b06..9a941eb 100644
--- a/README.md
+++ b/README.md
@@ -20,7 +20,7 @@ This project builds a chat server that:
 - Exposes a minimal, clean HTTP+JSON API — easy to build clients against
 - Supports multiple concurrent connections per user session
 - Provides IRC-like semantics: channels, nicks, topics, modes
-- Uses structured JSON messages with arbitrary extensibility
+- Uses structured JSON messages with IRC command names and numeric reply codes
 
 ## Architecture
 
@@ -38,6 +38,151 @@ request/response bodies. No WebSockets, no raw TCP, no gRPC — just plain HTTP.
 The entire read/write loop for a client is two endpoints. Everything else is
 channel management and history.
 
+### Message Protocol
+
+All messages use **IRC command names and numeric reply codes** from RFC 1459/2812.
+The `command` field identifies the message type.
+
+#### Message Envelope
+
+Every message is a JSON object with these fields:
+
+| Field     | Type            | Required | Description |
+|-----------|-----------------|----------|-------------|
+| `command` | string          | ✓        | IRC command name or 3-digit numeric code |
+| `from`    | string          |          | Sender nick or server name |
+| `to`      | string          |          | Destination: `#channel` or nick |
+| `params`  | array\<string\> |          | Additional IRC-style parameters |
+| `body`    | array \| object |          | Structured body (never a raw string) |
+| `meta`    | object          |          | Extensible metadata (signatures, etc.) |
+| `id`      | string (uuid)   |          | Server-assigned message ID |
+| `ts`      | string          |          | Server-assigned ISO 8601 timestamp |
+
+**Important:** Message bodies MUST be objects or arrays, never raw strings.
+This enables:
+- Multiline messages (array of lines)
+- Deterministic canonicalization for hashing/signing (RFC 8785 JCS)
+- Structured data where needed (e.g. PUBKEY)
+
+#### IRC Command Mapping
+
+**Client-to-Server (C2S):**
+
+| Command  | Description |
+|----------|-------------|
+| PRIVMSG  | Send message to channel or user |
+| NOTICE   | Send notice (no auto-reply expected) |
+| JOIN     | Join a channel |
+| PART     | Leave a channel |
+| QUIT     | Disconnect from server |
+| NICK     | Change nickname |
+| MODE     | Set/query channel or user modes |
+| TOPIC    | Set/query channel topic |
+| KICK     | Kick a user from a channel |
+| PING     | Client keepalive |
+| PUBKEY   | Announce public signing key |
+
+**Server-to-Client (S2C):**
+
+All C2S commands may be echoed back as S2C (relayed to other users), plus:
+
+| Command  | Description |
+|----------|-------------|
+| PONG     | Server keepalive response |
+| PUBKEY   | Relayed public key from another user |
+| ERROR    | Server error message |
+
+**Numeric Reply Codes (S2C):**
+
+| Code | Name              | Description |
+|------|-------------------|-------------|
+| 001  | RPL_WELCOME       | Welcome after registration |
+| 002  | RPL_YOURHOST      | Server host information |
+| 322  | RPL_LIST          | Channel list entry |
+| 353  | RPL_NAMREPLY      | Names list for a channel |
+| 366  | RPL_ENDOFNAMES    | End of names list |
+| 372  | RPL_MOTD          | Message of the day line |
+| 375  | RPL_MOTDSTART     | Start of MOTD |
+| 376  | RPL_ENDOFMOTD     | End of MOTD |
+| 401  | ERR_NOSUCHNICK    | No such nick or channel |
+| 403  | ERR_NOSUCHCHANNEL | No such channel |
+| 433  | ERR_NICKNAMEINUSE | Nickname already in use |
+
+**Server-to-Server (S2S):**
+
+| Command | Description |
+|---------|-------------|
+| RELAY   | Relay message to linked server |
+| LINK    | Establish server link |
+| UNLINK  | Tear down server link |
+| SYNC    | Synchronize state between servers |
+| PING    | Server-to-server keepalive |
+| PONG    | Server-to-server keepalive response |
+
+#### Message Examples
+
+```json
+{"command": "PRIVMSG", "from": "alice", "to": "#general", "body": ["hello world"], "meta": {"sig": "base64...", "alg": "ed25519"}}
+
+{"command": "PRIVMSG", "from": "alice", "to": "#general", "body": ["line one", "line two"]}
+
+{"command": "001", "to": "alice", "body": ["Welcome to the network, alice"]}
+
+{"command": "353", "to": "alice", "params": ["=", "#general"], "body": ["alice", "bob", "@charlie"]}
+
+{"command": "JOIN", "from": "bob", "to": "#general", "body": []}
+
+{"command": "ERROR", "body": ["Closing link: connection timeout"]}
+```
+
+#### JSON Schemas
+
+Full JSON Schema (draft 2020-12) definitions for all message types are in
+[`schema/`](schema/). See [`schema/README.md`](schema/README.md) for the
+complete index.
+
+### Canonicalization and Signing
+
+Messages support optional cryptographic signatures for integrity verification.
+
+#### Canonicalization (RFC 8785 JCS)
+
+To produce a deterministic byte representation of a message for signing:
+
+1. Remove `meta.sig` from the message (the signature itself is not signed)
+2. Serialize using [RFC 8785 JSON Canonicalization Scheme (JCS)](https://www.rfc-editor.org/rfc/rfc8785):
+   - Object keys sorted lexicographically
+   - No whitespace
+   - Numbers in shortest form
+   - UTF-8 encoding
+3. The resulting byte string is the signing input
+
+This is why `body` must be an object or array — raw strings would be ambiguous
+under canonicalization.
+
+#### Signing Flow
+
+1. Client generates an Ed25519 keypair
+2. Client announces public key: `{"command": "PUBKEY", "body": {"alg": "ed25519", "key": "base64..."}}`
+3. Server relays PUBKEY to channel members / stores for the session
+4. When sending a message, client:
+   a. Constructs the message without `meta.sig`
+   b. Canonicalizes per JCS
+   c. Signs with private key
+   d. Adds `meta.sig` (base64) and `meta.alg`
+5. Recipients verify by repeating steps a–c and checking the signature
+   against the sender's announced public key
+
+#### PUBKEY Message
+
+```json
+{"command": "PUBKEY", "from": "alice", "body": {"alg": "ed25519", "key": "base64-encoded-pubkey"}}
+```
+
+Servers SHOULD relay PUBKEY messages to all channel members. Clients SHOULD
+cache public keys and use them to verify `meta.sig` on incoming messages.
+Key distribution is trust-on-first-use (TOFU) by default.
+
 ### Core Concepts
 
 #### Users
@@ -63,36 +208,6 @@ channel management and history.
 - Channel history is stored server-side (configurable depth)
 - No eternal logging by default — history rotates
 
-#### Messages
-
-Every message is a structured JSON object:
-
-```json
-{
-  "id": "550e8400-e29b-41d4-a716-446655440000",
-  "ts": "2026-02-09T20:00:00.000Z",
-  "from": "nick",
-  "to": "#channel",
-  "type": "message",
-  "body": "Hello, world!",
-  "meta": {}
-}
-```
-
-Fields:
-- `id` — Server-assigned UUID, globally unique
-- `ts` — Server-assigned timestamp (ISO 8601)
-- `from` — Sender nick
-- `to` — Destination: channel name (`#foo`) or nick (for DMs)
-- `type` — Message type: `message`, `action`, `notice`, `join`, `part`, `quit`,
-  `topic`, `mode`, `nick`, `system`
-- `body` — Message content (UTF-8 text)
-- `meta` — Arbitrary extensible metadata (JSON object). Can carry:
-  - Cryptographic signatures
-  - Rich content hints (URLs, embeds)
-  - Client-specific extensions
-  - Reactions, edits, threading references
-
 ### API Endpoints
 
 All endpoints accept and return `application/json`. Authenticated endpoints
@@ -116,14 +231,14 @@ TOKEN=$(curl -s -X POST http://localhost:8080/api/v1/register \
   -d '{"nick":"alice"}' | jq -r .token)
 
 # Join a channel
-curl -s -X POST http://localhost:8080/api/v1/channels/join \
+curl -s -X POST http://localhost:8080/api/v1/messages \
   -H "Authorization: Bearer $TOKEN" \
-  -d '{"channel":"#general"}'
+  -d '{"command":"JOIN","to":"#general"}'
 
 # Send a message
 curl -s -X POST http://localhost:8080/api/v1/messages \
   -H "Authorization: Bearer $TOKEN" \
-  -d '{"to":"#general","content":"hello world"}'
+  -d '{"command":"PRIVMSG","to":"#general","body":["hello world"]}'
 
 # Poll for messages (long-poll)
 curl -s http://localhost:8080/api/v1/messages?after=0 \
@@ -149,8 +264,8 @@ GET  /api/v1/state           — User state: nick, id, and list of joined channe
 GET  /api/v1/messages        — Single message stream (long-poll supported)
                                 All message types: channel, DM, notices, events
                                 Query params: ?after=<message-id>&timeout=30
-POST /api/v1/messages        — Send a message
-                                Body: { "to": "#channel" or "nick", "content": "..." }
+POST /api/v1/messages        — Send a message (IRC command in body)
+                                Body: { "command": "PRIVMSG", "to": "#channel", "body": ["..."] }
 ```
 
 #### History
@@ -187,8 +302,9 @@ POST /api/v1/federation/relay    — Relay messages between linked servers
 GET  /api/v1/federation/status   — Link status
 ```
 
-Federation uses the same HTTP+JSON transport. Messages are relayed between
-servers so users on different servers can share channels.
+Federation uses the same HTTP+JSON transport. S2S messages use the RELAY, LINK,
+UNLINK, SYNC, PING, and PONG commands. Messages are relayed between servers so
+users on different servers can share channels.
 
 ### Channel Modes
 
@@ -239,44 +355,31 @@ Following [gohttpserver CONVENTIONS.md](https://git.eeqj.de/sneak/gohttpserver/s
 ```
 chat/
 ├── cmd/
-│   └── chat/
+│   └── chatd/
 │       └── main.go
 ├── internal/
 │   ├── config/
-│   │   └── config.go
 │   ├── database/
-│   │   └── database.go
 │   ├── globals/
-│   │   └── globals.go
 │   ├── handlers/
-│   │   ├── handlers.go
-│   │   ├── auth.go
-│   │   ├── channels.go
-│   │   ├── federation.go
-│   │   ├── healthcheck.go
-│   │   ├── messages.go
-│   │   └── users.go
 │   ├── healthcheck/
-│   │   └── healthcheck.go
 │   ├── logger/
-│   │   └── logger.go
 │   ├── middleware/
-│   │   └── middleware.go
 │   ├── models/
-│   │   ├── channel.go
-│   │   ├── message.go
-│   │   └── user.go
 │   ├── queue/
-│   │   └── queue.go
 │   └── server/
-│       ├── server.go
-│       ├── http.go
-│       └── routes.go
+├── schema/
+│   ├── message.schema.json
+│   ├── c2s/
+│   ├── s2c/
+│   ├── s2s/
+│   └── README.md
+├── web/
 ├── go.mod
 ├── go.sum
 ├── Makefile
 ├── Dockerfile
-├── CONVENTIONS.md → (copy from gohttpserver)
+├── CONVENTIONS.md
 └── README.md
 ```
 
@@ -298,26 +401,27 @@ Per gohttpserver conventions:
 ### Web Client
 
 The server embeds a single-page web client (Preact) served at `/`. This is a
-**convenience/reference implementation** — not the primary interface. It
-demonstrates the API and provides a quick way to test the server in a browser.
-
-The primary intended clients are IRC-style terminal applications and bots
-talking directly to the HTTP API.
+**convenience/reference implementation** — not the primary interface. The
+primary intended clients are IRC-style terminal applications, bots, and custom
+clients talking directly to the HTTP API.
 
 ### Design Principles
 
 1. **API-first** — the HTTP API is the product. Clients are thin. If you can't
    build a working IRC-style TUI client in an afternoon, the API is too complex.
-2. **HTTP is the only transport** — no WebSockets, no raw TCP, no protocol
+2. **IRC semantics over HTTP** — command names and numeric codes from RFC 1459/2812.
+   Familiar to anyone who's built IRC clients or bots.
+3. **HTTP is the only transport** — no WebSockets, no raw TCP, no protocol
    negotiation. HTTP is universal, proxy-friendly, and works everywhere.
-3. **Server holds state** — clients are stateless. Reconnect, switch devices,
+4. **Server holds state** — clients are stateless. Reconnect, switch devices,
    lose connectivity — your messages are waiting.
-4. **Structured messages** — JSON with extensible metadata. Enables signatures,
-   rich content, client extensions without protocol changes.
-5. **Simple deployment** — single binary, SQLite default, zero mandatory
+5. **Structured messages** — JSON with extensible metadata. Bodies are always
+   objects or arrays for deterministic canonicalization (JCS) and signing.
+6. **Simple deployment** — single binary, SQLite default, zero mandatory
    external dependencies.
-6. **No eternal logs** — history rotates. Chat should be ephemeral by default.
-7. **Federation optional** — single server works standalone. Linking is opt-in.
+7. **No eternal logs** — history rotates. Chat should be ephemeral by default.
+8. **Federation optional** — single server works standalone. Linking is opt-in.
+9. **Signable messages** — optional Ed25519 signatures with TOFU key distribution.
 
 ## Status