Thingctx MCP Server

thingctx

thingctx turns a description of any API, device, or local process into tools an AI agent can call: authorized per operation, over the system's own transport, and the agent never holds your keys. The description is a W3C Web of Things Thing Description (a TD), a plain JSON file naming what the system can do. Write one, or compile it from an OpenAPI spec. The described system is the server, so you run no server per integration.

A "Thing" is whatever you want to describe: a REST API, an app, a sensor, a media server, a local object, or one system that is several of those at once. A media server takes commands over HTTP and serves its stream over RTSP. The pump in examples/ reads over MQTT and acts through a local call. Each is one Thing and one description.

A description names actions, properties, and events, and gives each one a form: the entry that says where and how to reach it. The URL scheme in that address picks the transport per call, so however many protocols one Thing spans, the agent still sees one tool set.

docs/BINDINGS.md covers the transports and how to add your own. A subprocess transport, exec, also ships, and it ships locked: it refuses every command until you hand it an explicit allowlist.

Those three stay distinct all the way to the call. A read, a write, and a subscribe do not collapse into one undifferentiated function, which is why the gate can allow the read and refuse the write on the same system. A flat list of functions has no such handle.

Pick your path: use it as a library if you own the agent loop, the command line if you do not want to write code, the MCP bridge if your host only speaks MCP, or add a transport if thingctx does not speak your protocol yet.

Stuck, or wondering whether something is possible? Ask in Discussions. Want to build something small? The open issues say what would help.

First run: no keys, no network

One paste shows the whole idea. The description is inline and the handler ships with the package, so nothing here needs a key, a network, or a second file:

pip install thingctx

import asyncio

import thingctx
from thingctx.contrib.time import make_time_handler

TD = {
    "@context": "https://www.w3.org/2022/wot/td/v1.1",
    "id": "urn:thingctx:time",
    "title": "Time",
    "securityDefinitions": {"nosec_sc": {"scheme": "nosec"}},
    "security": ["nosec_sc"],
    "actions": {
        "getCurrentTime": {
            "description": "Current time in an IANA timezone (default UTC).",
            "input": {
                "type": "object",
                "properties": {"timezone": {"type": "string"}},
            },
            "safe": True,
            "idempotent": True,
            "forms": [{"href": "local://getCurrentTime"}],
        }
    },
}


async def main():
    client = thingctx.ThingClient(
        tds=[TD], bindings=[thingctx.LocalBinding(make_time_handler())]
    )
    tools, invoke = client.as_tools()  # specs for your model; invoke runs a call
    print("tools:", [t["function"]["name"] for t in tools])
    print(await invoke("time__getCurrentTime", {"timezone": "UTC"}))


asyncio.run(main())

tools: ['time__getCurrentTime']
{'timezone': 'UTC', 'datetime': '2026-07-26T15:59:03.233080+00:00', 'utc_offset': '+0000'}

That is the whole loop: a description in, tools out, calls routed. LocalBinding is a binding, a transport implementation; this one routes the local:// address to the handler you pass it. Every other transport works the same way; only the form's href changes.

Install

pip install 'thingctx[llm,http,validate]'

Quote the argument; unquoted brackets fail in zsh. Base pip install thingctx has no dependencies; it already includes the local and exec transports. Every optional transport and capability has an extra, listed in pyproject.toml; each one this page uses is named next to the code that needs it.

The document

A description can be small. This one drives the live, key free Open-Meteo forecast API, so it runs as written. Save it as weather.td.json, a later example uses it:

{
  "@context": "https://www.w3.org/2022/wot/td/v1.1",
  "id": "urn:example:weather:v1",
  "title": "Weather",
  "securityDefinitions": { "nosec_sc": { "scheme": "nosec" } },
  "security": ["nosec_sc"],
  "actions": {
    "forecast": {
      "input": {
        "type": "object",
        "properties": {
          "latitude": { "type": "number" },
          "longitude": { "type": "number" },
          "current": { "type": "string" }
        },
        "required": ["latitude", "longitude"]
      },
      "forms": [{ "href": "https://api.open-meteo.com/v1/forecast", "htv:methodName": "GET" }]
    }
  }
}

thingctx projects each action to a tool named <thing>__<action>: this file yields weather__forecast (a version segment on the id is dropped). docs/MAPPING.md specifies the full projection. The description carries no secrets, so it is safe to commit and share. The secret is supplied at runtime to the binding that carries the call. Secrets are keyed per Thing.

If your system already has an OpenAPI 3.x spec, you do not have to author a description at all:

pip install 'thingctx[openapi]'
thingctx import openapi https://api.example.com/openapi.json --out api.td.json

The spec can be a file or a URL, JSON or YAML; --base-url, --id, and --title override what the spec says. The result is a normal description, so everything else here applies to it unchanged.

Ready made descriptions for common apps, developer tools, and devices live at td.thingctx.com.

Use it as a library

Own the agent loop? Read descriptions, hand the specs to your model, and route each call back through invoke. ThingClient needs no LLM and has no opinion on what chose the action; any code can drive it. This sketch shows the surface against a folder describing a pump; from_arg turns a path or URL into a registry of descriptions:

import thingctx


async def run():  # a sketch, not a program: call it from your own loop
    client = thingctx.ThingClient.from_registry(thingctx.from_arg("./descriptions/"))
    specs, invoke = client.as_tools()

    await invoke("pump__set_speed", {"rpm": 1500})
    await client.read_property("pump__rpm")
    await client.write_property("pump__target_rpm", 1500)   # gated like invoke
    async for evt in await client.subscribe("pump__overheat"):  # subscribe returns an async iterator
        ...

The form picks the transport per call, so one client can read over HTTP and subscribe over MQTT. Bindings that pull optional dependencies, MQTT among them, are off by default: install the extra and pass bindings=thingctx.BindingRegistry.default(mqtt=True).

Want the loop handled for you? The llm extra runs any provider through litellm; add the http extra, since the weather file's form is HTTPS. Set your provider key in its usual variable (OPENAI_API_KEY, ANTHROPIC_API_KEY, and so on) and pick a model with THINGCTX_MODEL:

import asyncio
import thingctx


async def main():
    # weather.td.json from above; it points at a live, key free API
    host = thingctx.from_file("weather.td.json")
    print(await host.chat("What is the forecast for Cairo? Latitude 30.0, longitude 31.2."))


asyncio.run(main())

The model calls weather__forecast itself and answers in prose:

The forecast for Cairo is clear, around 34 C.

Safety: approval and authorization

Two opt in layers stand between an agent and a real system; both run before any transport is selected. Neither layer handles a credential. The binding holds the secret and the model never sees it.

Approval gates risky calls behind a human. Risk is read from the description, and when to gate is yours: declared (only actions the description marks risky; the default), destructive (adds non idempotent actions and every property write), all, or never. A gated call with no approver is denied: a gate with nobody to open it stays shut. The check sits inside invoke and write_property, so it covers the LLM loop, direct callers, and the MCP bridge alike.

Carrying on from the first example above, with the same TD:

def approve(req):  # sync or async; return True to allow
    return input(f"run {req.tool_name}{req.arguments}? [y/N] ").lower() == "y"

client = thingctx.ThingClient(
    tds=[TD],
    bindings=[thingctx.LocalBinding(make_time_handler())],
    approve=approve,
    approve_when="all",
)

Authorization decides from policy, per caller, per operation. Pass a pdp and an identity and every call authorizes the resolved (thing, affordance, operation) before it reaches the system; an affordance is an action, property, or event named in the description. This snippet condenses examples/14_authz.py, which runs as is on the core install. It defines the TD and Pump used below: a pump with one property, target_rpm.

from thingctx import LocalBinding, ThingClient
from thingctx.authz import LocalPolicyGrantSource, PolicyDecisionPoint, build_vocabulary

reader = ThingClient(tds=[TD], bindings=[LocalBinding(Pump())])  # no pdp yet; parsed only to read the description
vocab = build_vocabulary(reader.things)  # the closed set the description declares

grants = LocalPolicyGrantSource(
    {"operator": {("urn:demo:pump", "target_rpm", "readproperty")}}
)
pdp = PolicyDecisionPoint(vocabulary=vocab, grant_source=grants)
identity = {"sub": "alice", "roles": ["operator"]}  # claims, validated upstream

client = ThingClient(
    tds=[TD], bindings=[LocalBinding(Pump())], pdp=pdp, identity=identity
)

Alice's operator role grants read on target_rpm and nothing else, so her reads pass and her writes are refused. The vocabulary is closed: a grant is honored only for operations the description declares. thingctx.authz imports no crypto and runs on the dependency free core. Identity is claims that something upstream validated, never the credential itself.

Running the example prints:

vocabulary (grantable tuples the TD declares):
  (urn:demo:pump, target_rpm, readproperty)
  (urn:demo:pump, target_rpm, writeproperty)

READ  target_rpm  -> ALLOWED, device returned 1200
WRITE target_rpm  -> DENIED, grant does not include ('urn:demo:pump', 'target_rpm', 'writeproperty')

RE-READ target_rpm -> 1200  (unchanged: the denied write never ran)

The full model is in docs/SECURITY.md.

The MCP bridge

Some agents only take tools over MCP. For those, thingctx ships one generic MCP server, with no per integration server. It serves any registry of descriptions: a folder, a URL, or a W3C Thing Description Directory. A Directory is the standard catalog server for descriptions.

pip install 'thingctx[mcp,http]'
thingctx-mcp ./descriptions/

For Claude Desktop, add this to ~/Library/Application Support/Claude/claude_desktop_config.json (on Windows: %APPDATA%\Claude\claude_desktop_config.json) and restart:

{ "mcpServers": { "things": {
  "command": "thingctx-mcp",
  "args": ["/path/to/your/descriptions/"],
  "env": { "THINGCTX_APPROVE_WHEN": "destructive" } } } }

The same approval gate applies here: the bridge marks risky tools and asks the client to confirm. Declining denies the call. A client that cannot show a confirmation dialog gets the call parked as pending instead, and the bridge's approve tool confirms it from the chat. THINGCTX_APPROVE_WHEN picks the policy, and THINGCTX_POLICY set to read-only denies writes and state changing actions outright.

Descriptions never carry secrets, so the bridge reads them from the environment: THINGCTX_TOKEN_<SLUG> binds a secret to the Thing with that slug (THINGCTX_TOKEN_GITHUB serves github), applied per the Thing's declared scheme.

The command line

The thingctx command drives the same runtime from a terminal. Point list and invoke at any folder of descriptions. Save the TD from the first run above as things/time.td.json, then:

thingctx list ./things/
thingctx invoke ./things/ time__getCurrentTime --arg timezone=UTC

{
  "timezone": "UTC",
  "datetime": "2026-07-26T16:45:57.114817+00:00",
  "utc_offset": "+0000"
}

That works with no extra wiring because the clock's handler ships with the package and binds to the urn:thingctx:time id in the description.

list prints every tool the folder's Things expose, with its schema; invoke runs one action. thingctx --help lists the other subcommands, including the OpenAPI importer shown above. invoke honors the same approval gate. --approve-when picks the policy (THINGCTX_APPROVE_WHEN is the fallback), -y approves without a prompt, and with no terminal and no -y a gated call is denied with a non zero exit. An agent shelling out gets the same protection as one holding the library.

Extend it

Describing a new system needs nothing from this repo. Teaching thingctx something it does not know yet is one class, and every part works the same way, so what you learn once applies to the rest.

A transport is the common case:

class CoapBinding:
    scheme = "coap"

    async def invoke(self, action, form, arguments): ...   # required
    async def read(self, prop, form): ...                  # optional

The contract is a scheme plus an async invoke. Add read, write, or subscribe if the transport supports them; the runtime checks which methods exist before calling, so a pub sub transport without reads simply has none. Pass the binding to the client and it is live. Registering one for a scheme thingctx already serves replaces the built in binding.

The same shape covers the rest:

Each contract is a typing.Protocol: match the methods, inherit nothing. @implements(Contract) checks the match at import time, and the conformance kit in thingctx.testing checks the runtime behaviour a type checker cannot. examples/13_custom_stack.py builds one of each in a single file, offline.

Keep what you write private in your own package, or contribute it so nobody writes it twice. Out of tree packages register through entry points and are discovered without a fork. See docs/BINDINGS.md.

Interoperability

thingctx consumes a description no matter who produced it. Demos under examples/interop/ prove it end to end: Eclipse Thingweb's node-wot serves a Thing and thingctx drives it; Eclipse Ditto generates a description for a digital twin and thingctx round trips state through it. The Thing Description is a W3C Recommendation, so a file you write here is portable to any other WoT consumer, and thingctx reads a W3C Thing Description Directory.

Contributing

Driving your own system needs nothing from this repo: write a description and point thingctx at it. What the project does need is transports it cannot speak yet, and each one is a single class.

Good places to start:

• good first issue is scoped work with the context written down. Comment to claim one and it gets assigned to you.
• help wanted is everything else that is open.
• CONTRIBUTING.md explains how a binding fits together.

Contributor patches have added a lint rule and closed a coverage gap. Small, scoped, merged.

Every commit needs a DCO Signed-off-by line, which git commit -s adds. AI assisted patches are welcome; a real human reviews and signs off.

Questions do not need an issue. Discussions is the place for "does this already do X", "would you take a PR for Y", and how to reach a system you have. Asking there is useful even when the answer is no, because it tells the project what people are trying to do.

License

Apache 2.0. See LICENSE.