diff --git a/README.md b/README.md
index b480fc7..6ff171d 100644
--- a/README.md
+++ b/README.md
@@ -1,3 +1,41 @@
-# skill-openclaw-channel
+# openclaw-channel plugin
 
-Hermes plugin: send_to_agent tool for inter-agent relay messaging
\ No newline at end of file
+**Critical infrastructure.** This plugin provides the `send_to_agent` tool — the only way agents can send messages to each other through the relay.
+
+## What it does
+
+Registers a single tool (`send_to_agent`) with Hermes' tool registry. The tool POSTs messages to the relay on www0, which routes them to the target agent's webhook.
+
+## Why it matters
+
+Without this plugin, agents cannot communicate with each other. Inter-agent coordination, delegation, and status reporting all depend on it.
+
+**Do not remove this plugin.** It was accidentally deleted once (2026-05-09) and broke all inter-agent messaging until restored.
+
+## Files
+
+| File | Purpose |
+|------|---------|
+| `__init__.py` | Plugin entrypoint — registers the tool with Hermes |
+| `send_to_agent.py` | Tool implementation — schema, handler, auth |
+| `plugin.yaml` | Plugin metadata |
+| `README.md` | This file |
+
+## Environment variables
+
+| Variable | Description | Example |
+|----------|-------------|---------|
+| `OPENCLAW_AGENT_ID` | This agent's name | `bastion` |
+| `OPENCLAW_RELAY_URL` | Relay ingress URL | `http://www0:4100` |
+| `OPENCLAW_RELAY_SECRET` | Auth secret for relay | (set in container .env) |
+
+## Message types
+
+- `fyi` — informational, no reply expected (default)
+- `request` — recipient should reply
+- `ack` — acknowledging a prior message; terminal
+
+## Relay docs
+
+Full architecture: `/opt/data/docs/hermes-comms-bridge.md`
+Relay skill: `hermes-relay`
diff --git a/__init__.py b/__init__.py
new file mode 100644
index 0000000..e3a519a
--- /dev/null
+++ b/__init__.py
@@ -0,0 +1,26 @@
+"""openclaw-channel plugin.
+
+Registers the send_to_agent tool for inter-agent messaging via openclaw-relay.
+
+See send_to_agent.py for tool implementation and README.md for context.
+"""
+from __future__ import annotations
+
+import logging
+
+logger = logging.getLogger(__name__)
+
+
+def register(ctx):
+    from .send_to_agent import _send, _check, SEND_SCHEMA, AGENT_ID
+
+    ctx.register_tool(
+        name="send_to_agent",
+        toolset="openclaw",
+        schema=SEND_SCHEMA,
+        handler=_send,
+        check_fn=_check,
+        description="Send a message to another fleet agent via openclaw-relay.",
+        emoji="📡",
+    )
+    logger.info("openclaw-channel: registered send_to_agent (agent=%s)", AGENT_ID)
diff --git a/plugin.yaml b/plugin.yaml
new file mode 100644
index 0000000..6cd2e74
--- /dev/null
+++ b/plugin.yaml
@@ -0,0 +1,5 @@
+name: openclaw-channel
+version: 0.1.0
+description: "openclaw-relay inter-agent channel — adds send_to_agent tool for fleet messaging"
+provides_tools:
+  - send_to_agent
diff --git a/send_to_agent.py b/send_to_agent.py
new file mode 100644
index 0000000..50a482b
--- /dev/null
+++ b/send_to_agent.py
@@ -0,0 +1,131 @@
+"""send_to_agent — inter-agent messaging via openclaw-relay.
+
+This tool is the OUTBOUND half of the relay channel. It lets agents send
+messages to other fleet agents through the relay on www0.
+
+INBOUND messages arrive via the webhook platform (config.yaml →
+platforms.webhook.routes.openclaw), delivered by the relay to each
+agent's webhook endpoint.
+
+CRITICAL: This tool is how agents talk to each other. Without it,
+inter-agent coordination is dead. Do NOT remove or rename without
+replacing the functionality.
+
+Environment variables required:
+  OPENCLAW_AGENT_ID   — this agent's name (e.g. "bastion", "vigil")
+  OPENCLAW_RELAY_URL  — relay ingress URL (e.g. http://www0:4100)
+  OPENCLAW_RELAY_SECRET — auth secret for relay ingress
+"""
+from __future__ import annotations
+
+import json
+import logging
+import os
+from typing import Any
+from urllib import error as urlerror, request as urlrequest
+
+from tools.registry import tool_error
+
+logger = logging.getLogger(__name__)
+
+AGENT_ID = os.environ.get("OPENCLAW_AGENT_ID", "bastion")
+RELAY_URL = os.environ.get("OPENCLAW_RELAY_URL", "http://www0:4100").rstrip("/")
+SECRET = (os.environ.get("OPENCLAW_RELAY_SECRET") or "").strip()
+
+KNOWN_AGENTS = [
+    "atlas", "bastion", "claude_memgpt", "clio", "ferret", "flux",
+    "mint", "nene", "piper", "reed", "scout", "skippy", "tangent",
+    "terra", "vera", "vigil",
+]
+
+SEND_SCHEMA = {
+    "name": "send_to_agent",
+    "description": (
+        f"Send a message to another fleet agent via openclaw-relay as "
+        f"{AGENT_ID}.\n\n"
+        "Types:\n"
+        "- fyi: informational, no reply expected (default)\n"
+        "- request: the recipient should reply\n"
+        "- ack: acknowledging a prior message; terminal\n\n"
+        f"Known agents: {', '.join(KNOWN_AGENTS)}.\n"
+        "Returns the relay's JSON response (delivered/queued/error)."
+    ),
+    "parameters": {
+        "type": "object",
+        "properties": {
+            "to": {
+                "type": "string",
+                "description": "Target agent name (lowercase). Example: terra, claude_memgpt.",
+            },
+            "message": {
+                "type": "string",
+                "description": "Message body to send.",
+            },
+            "type": {
+                "type": "string",
+                "enum": ["fyi", "request", "ack"],
+                "default": "fyi",
+                "description": "Message classification.",
+            },
+            "project": {
+                "type": "string",
+                "description": "Optional project tag for relay-side grouping/filtering.",
+            },
+            "inReplyTo": {
+                "type": "string",
+                "description": "Optional messageId being replied to.",
+            },
+        },
+        "required": ["to", "message"],
+    },
+}
+
+
+def _send(args: dict, **kwargs: Any) -> str:
+    to = str(args.get("to") or "").lower().strip()
+    message = args.get("message")
+    if not to or not message:
+        return tool_error("to and message are required")
+    if not SECRET:
+        return tool_error(
+            "OPENCLAW_RELAY_SECRET not set; cannot authenticate to openclaw-relay"
+        )
+
+    body: dict[str, Any] = {
+        "from": AGENT_ID,
+        "to": to,
+        "type": args.get("type") or "fyi",
+        "body": message,
+    }
+    if args.get("project"):
+        body["project"] = args["project"]
+    if args.get("inReplyTo"):
+        body["inReplyTo"] = args["inReplyTo"]
+
+    raw = json.dumps(body).encode("utf-8")
+    req = urlrequest.Request(
+        f"{RELAY_URL}/msg",
+        data=raw,
+        method="POST",
+        headers={
+            "content-type": "application/json",
+            "x-relay-agent": AGENT_ID,
+            "x-relay-secret": SECRET,
+        },
+    )
+    try:
+        with urlrequest.urlopen(req, timeout=15) as resp:
+            return resp.read().decode("utf-8", errors="replace")
+    except urlerror.HTTPError as e:
+        detail = ""
+        try:
+            detail = e.read().decode("utf-8", errors="replace")[:500]
+        except Exception:
+            pass
+        return tool_error(f"relay HTTP {e.code}", detail=detail)
+    except Exception as e:
+        return tool_error(f"relay request failed: {e}")
+
+
+def _check() -> bool:
+    return bool(SECRET)