Plugins - loom

Loom supports optional plugins via .use(...). Plugins add behavior without modifying core code.

Plugin Protocol

A plugin is any Python class implementing optional methods (no base class required):

Hook	Triggered	Purpose
`on_register(loom)`	On `.use()`	Plugin initialization
`before_build(state, registry)`	Before `build()`	Pre-processing
`after_build(state, registry, result)`	After `build()`	Post-processing
`before_chat(state, registry)`	Before `chat()`	Pre-processing
`after_chat(state, registry, result, answer)`	After `chat()`	Post-processing
`chat_prompt_vars(message, *, session_id, state, registry, recalled)`	During chatbot prompt generation	Inject custom prompt variables

Plugins use best-effort isolation: any plugin exception will never crash the core pipeline.

Registering Plugins

loom = (
    Loom(config)
    .register(schema)
    .cm_prompt(default_cm_prompt)
    .chatbot_prompt(DEFAULT_CHATBOT_PROMPT)
    .use(MyPlugin())
)

Example: External RAG Plugin

A complete example that retrieves context from an external service and injects it into the chatbot prompt:

import asyncio
import json
from urllib.request import Request, urlopen

from loom import Loom, LoomConfig, UniversalSchemaDomain
from loom.prompts import default_cm_prompt, DEFAULT_CHATBOT_PROMPT


class ExternalRAGPlugin:
    name = "external_rag"

    def __init__(self, endpoint: str):
        self.endpoint = endpoint.rstrip("/")

    async def chat_prompt_vars(self, message, *, session_id, state, registry, recalled):
        payload = json.dumps({"query": message, "session_id": session_id}).encode()
        req = Request(
            url=f"{self.endpoint}/retrieve",
            data=payload,
            headers={"Content-Type": "application/json"},
            method="POST",
        )

        def _do():
            with urlopen(req, timeout=15) as resp:
                data = json.loads(resp.read().decode())
            return (data.get("context") or "").strip()

        ctx = await asyncio.to_thread(_do)
        if not ctx:
            return {}
        return {"rag_section": f"## Retrieved Context (RAG)\n{ctx}\n"}


config = LoomConfig.from_file()
schema = UniversalSchemaDomain("user_profile")
schema.create_field("identity.name", "", "User's name")

loom = (
    Loom(config)
    .register(schema)
    .cm_prompt(default_cm_prompt)
    .chatbot_prompt(DEFAULT_CHATBOT_PROMPT)  # supports {rag_section}
    .use(ExternalRAGPlugin("http://localhost:9000"))
)

Common Use Cases

External RAG retrieval — call your own service, inject retrieved context
Logging / metrics — track build and chat operations
Safety filters / policy checks — validate inputs and outputs

​Plugin Protocol

​Registering Plugins

​Example: External RAG Plugin

​Common Use Cases

Plugin Protocol

Registering Plugins

Example: External RAG Plugin

Common Use Cases