diff --git a/README.md b/README.md
index c4508cb..a451048 100644
--- a/README.md
+++ b/README.md
@@ -53,3 +53,49 @@ To install any optional dependencies, such as development dependencies, use:
 ```bash
 pip install -e .[dev]
 ```
+
+## Keywords
+
+A **keyword** is a typed named value served over libby, with a uniform payload convention:
+
+- `{}` → show (return current value)
+- `{"value": V}` → modify (apply, then return it)
+
+Types: `BoolKeyword`, `IntKeyword`, `FloatKeyword`, `StringKeyword`,
+`TriggerKeyword`. Access mode is inferred — pass a `getter` for
+read-only, a `setter` for write-only, both for read-write. Optional
+extras: `units`, `description`, `nullable`, `validator`.
+
+```python
+from libby import Libby, BoolKeyword, FloatKeyword, TriggerKeyword
+
+libby = Libby.rabbitmq(self_id="my-peer", rabbitmq_url="amqp://localhost")
+
+state = {"position": 0.0}
+libby.register_keywords([
+    BoolKeyword("online", getter=lambda: True),
+    FloatKeyword("position",
+                 getter=lambda: state["position"],
+                 setter=lambda v: state.update(position=v),
+                 units="mm"),
+    TriggerKeyword("halt", action=lambda: print("halted")),
+])
+```
+
+Clients call the keyword by name:
+
+```python
+client = Libby.rabbitmq(self_id="client", rabbitmq_url="amqp://localhost")
+
+client.rpc("my-peer", "position", {})               # show
+client.rpc("my-peer", "position", {"value": 12.5})  # modify
+client.rpc("my-peer", "halt", {"value": 1})         # fire
+```
+
+Two meta-services are auto-registered on every peer that uses the
+keyword registry:
+
+- `keys.list` — payload `{"pattern": "..."}` (default `"%"`) → names,
+  sorted. `%` wildcards within a single name.
+- `keys.describe` — payload `{"name": "..."}` → flat metadata dict.
+  Exact lookup; no wildcards.
diff --git a/libby/__init__.py b/libby/__init__.py
index 8562ce6..6e30b3e 100644
--- a/libby/__init__.py
+++ b/libby/__init__.py
@@ -1,7 +1,27 @@
 from bamboo.protocol import Protocol
 from bamboo.builder import MessageBuilder
 from bamboo.keys import KeyRegistry
-from .zmq_transport import ZmqTransport
 from .libby import Libby
+from .keyword import (
+    Keyword,
+    BoolKeyword,
+    IntKeyword,
+    FloatKeyword,
+    StringKeyword,
+    TriggerKeyword,
+    match_pattern,
+)
 
-__all__ = ["Libby", "ZmqTransport", "Protocol", "MessageBuilder", "KeyRegistry"]
+__all__ = [
+    "Libby",
+    "Protocol",
+    "MessageBuilder",
+    "KeyRegistry",
+    "Keyword",
+    "BoolKeyword",
+    "IntKeyword",
+    "FloatKeyword",
+    "StringKeyword",
+    "TriggerKeyword",
+    "match_pattern",
+]
diff --git a/libby/keyword.py b/libby/keyword.py
new file mode 100644
index 0000000..756ddb8
--- /dev/null
+++ b/libby/keyword.py
@@ -0,0 +1,210 @@
+"""Keyword classes for Libby."""
+from __future__ import annotations
+
+import re
+from typing import Any, Callable, Iterable, List, Optional
+
+Getter = Callable[[], Any]
+Setter = Callable[[Any], None]
+Validator = Callable[[Any], Optional[str]]
+Action = Callable[[], None]
+
+
+def match_pattern(pattern: str, names: Iterable[str]) -> List[str]:
+    """Return names matching ``pattern``, sorted. ``%`` is a wildcard;
+    it matches any run of characters excluding ``.``."""
+    parts = pattern.split("%")
+    rx = re.compile("^" + "[^.]*".join(re.escape(p) for p in parts) + "$")
+    return sorted(n for n in names if rx.match(n))
+
+
+class Keyword:
+    """Named value exposed as a libby service."""
+
+    type_name: str = "any"
+
+    def __init__(
+        self,
+        name: str,
+        *,
+        getter: Optional[Getter] = None,
+        setter: Optional[Setter] = None,
+        units: Optional[str] = None,
+        description: str = "",
+        nullable: bool = False,
+        validator: Optional[Validator] = None,
+    ) -> None:
+        if getter is None and setter is None:
+            raise ValueError(
+                f"keyword '{name}' must supply at least one of getter/setter"
+            )
+        self.name = name
+        self._getter = getter
+        self._setter = setter
+        self.units = units
+        self.description = description
+        self.nullable = nullable
+        self._validator = validator
+
+    @property
+    def readonly(self) -> bool:
+        return self._setter is None
+
+    @property
+    def writeonly(self) -> bool:
+        return self._getter is None
+
+    def _type_check(self, v: Any) -> Any:
+        """Type-check or cast ``v``. Override per subclass."""
+        return v
+
+    def _response(self, value: Any) -> dict:
+        out: dict[str, Any] = {"ok": True, "value": value}
+        if self.units is not None:
+            out["units"] = self.units
+        return out
+
+    def describe(self) -> dict:
+        out: dict[str, Any] = {
+            "name": self.name,
+            "type": self.type_name,
+            "readonly": self.readonly,
+            "writeonly": self.writeonly,
+            "nullable": self.nullable,
+        }
+        if self.units is not None:
+            out["units"] = self.units
+        if self.description:
+            out["description"] = self.description
+        return out
+
+    def handle(self, payload: dict) -> dict:
+        if "value" in payload:
+            return self._modify(payload["value"])
+        return self._show()
+
+    def _show(self) -> dict:
+        if self.writeonly:
+            return {"ok": False, "error": "keyword is write-only"}
+        try:
+            value = self._getter()  # type: ignore[misc]
+        except Exception as e:
+            return {"ok": False, "error": str(e)}
+        return self._response(value)
+
+    def _modify(self, raw: Any) -> dict:
+        if self.readonly:
+            return {"ok": False, "error": "keyword is read-only"}
+        if raw is None:
+            if not self.nullable:
+                return {"ok": False, "error": f"value must be {self.type_name}"}
+            value: Any = None
+        else:
+            try:
+                value = self._type_check(raw)
+            except (TypeError, ValueError) as e:
+                return {"ok": False, "error": str(e)}
+            if self._validator is not None:
+                verr = self._validator(value)
+                if verr:
+                    return {"ok": False, "error": verr}
+        try:
+            self._setter(value)  # type: ignore[misc]
+        except Exception as e:
+            return {"ok": False, "error": str(e)}
+        return self._response(value)
+
+
+class BoolKeyword(Keyword):
+    """Keyword whose value is a Python ``bool``."""
+
+    type_name = "bool"
+
+    def _type_check(self, v: Any) -> bool:
+        if not isinstance(v, bool):
+            raise TypeError("value must be a bool")
+        return v
+
+
+class IntKeyword(Keyword):
+    """Keyword whose value is a Python ``int``; ``bool`` is rejected."""
+
+    type_name = "int"
+
+    def _type_check(self, v: Any) -> int:
+        # bool is a subclass of int in Python; reject explicitly
+        if isinstance(v, bool) or not isinstance(v, int):
+            raise TypeError("value must be an int")
+        return v
+
+
+class FloatKeyword(Keyword):
+    """Keyword whose value is a Python ``float``; accepts ``int``, rejects ``bool``."""
+
+    type_name = "float"
+
+    def _type_check(self, v: Any) -> float:
+        if isinstance(v, bool) or not isinstance(v, (int, float)):
+            raise TypeError("value must be a number")
+        return float(v)
+
+
+class StringKeyword(Keyword):
+    """Keyword whose value is a Python ``str``."""
+
+    type_name = "string"
+
+    def _type_check(self, v: Any) -> str:
+        if not isinstance(v, str):
+            raise TypeError("value must be a string")
+        return v
+
+
+class TriggerKeyword(Keyword):
+    """Write-only action keyword. Any modify fires ``action``; show returns ``false``."""
+
+    type_name = "trigger"
+
+    def __init__(
+        self,
+        name: str,
+        *,
+        action: Action,
+        description: str = "",
+    ) -> None:
+        self.name = name
+        self._action = action
+        self._getter = None
+        self._setter = None
+        self.units = None
+        self.description = description
+        self.nullable = False
+        self._validator = None
+
+    @property
+    def readonly(self) -> bool:
+        return False
+
+    @property
+    def writeonly(self) -> bool:
+        return True
+
+    def handle(self, payload: dict) -> dict:
+        if "value" not in payload:
+            return {"ok": True, "value": False}
+        try:
+            self._action()
+        except Exception as e:
+            return {"ok": False, "error": str(e)}
+        return {"ok": True, "value": True}
+
+
+__all__ = [
+    "Keyword",
+    "BoolKeyword",
+    "IntKeyword",
+    "FloatKeyword",
+    "StringKeyword",
+    "TriggerKeyword",
+    "match_pattern",
+]
diff --git a/libby/libby.py b/libby/libby.py
index f55a194..7bb8f93 100644
--- a/libby/libby.py
+++ b/libby/libby.py
@@ -1,11 +1,13 @@
 from __future__ import annotations
-from typing import Callable, Dict, List, Optional, Any
+from typing import Any, Callable, Dict, Iterable, List, Optional
 import time
 
 from bamboo.keys import KeyRegistry
 from bamboo.protocol import Protocol
 from bamboo.discovery import Discovery
 
+from .keyword import Keyword, match_pattern
+
 class Libby:
     def __init__(
         self,
@@ -42,6 +44,10 @@ def __init__(
                         pass
             self._disco.start()
 
+        self._keywords: Dict[str, Keyword] = {}
+        self.serve_keys(["keys.list"], self._keys_list)
+        self.serve_keys(["keys.describe"], self._keys_describe)
+
     @classmethod
     def zmq(
         cls,
@@ -159,6 +165,45 @@ def serve_keys(self, keys: List[str], callback: Callable[[dict, dict], Optional[
         for k in keys:
             self.proto.serve(k, callback)
 
+    def register_keyword(self, keyword: Keyword) -> None:
+        if keyword.name in self._keywords:
+            raise ValueError(f"keyword '{keyword.name}' already registered")
+        self._keywords[keyword.name] = keyword
+        self.serve_keys([keyword.name], self._keyword_dispatcher)
+
+    def register_keywords(self, keywords: Iterable[Keyword]) -> None:
+        keywords = list(keywords)
+        for keyword in keywords:
+            if keyword.name in self._keywords:
+                raise ValueError(f"keyword '{keyword.name}' already registered")
+            self._keywords[keyword.name] = keyword
+        if keywords:
+            self.serve_keys([k.name for k in keywords], self._keyword_dispatcher)
+
+    def _keyword_dispatcher(self, payload: dict, ctx: dict) -> dict:
+        keyword = self._keywords.get(ctx.get("key", ""))
+        if keyword is None:
+            return {"ok": False, "error": f"unknown keyword '{ctx.get('key', '')}'"}
+        try:
+            return keyword.handle(payload)
+        except Exception as e:
+            return {"ok": False, "error": str(e)}
+
+    def _keys_list(self, payload: dict, _ctx: dict) -> dict:
+        pattern = payload.get("pattern", "%")
+        if not isinstance(pattern, str):
+            return {"ok": False, "error": "pattern must be a string"}
+        return {"ok": True, "matches": match_pattern(pattern, self._keywords)}
+
+    def _keys_describe(self, payload: dict, _ctx: dict) -> dict:
+        name = payload.get("name")
+        if not isinstance(name, str) or not name:
+            return {"ok": False, "error": "name must be a non-empty string"}
+        keyword = self._keywords.get(name)
+        if keyword is None:
+            return {"ok": False, "error": f"unknown keyword '{name}'"}
+        return {"ok": True, **keyword.describe()}
+
     def listen(self, topic: str, handler: Callable[[Any], None]) -> None:
         self.proto.listen(topic, handler)