Nmos

An MCP server for AMWA NMOS. It connects to an NMOS Registry, lets an agent query everything on the network (IS-04) and — the headline feature — connect senders to receivers to route media between devices (IS-05).

• IS-04 (Discovery & Registration) — read Nodes, Devices, Senders, Receivers, Flows, Sources and Subscriptions from the registry's Query API.
• IS-05 (Device Connection Management) — connect/disconnect, enable/disable senders, inspect staged/active state, and bulk-route.
• Works against a plain-HTTP lab registry or an HTTPS deployment with IS-10 OAuth2 bearer tokens.
• Finds the registry from NMOS_REGISTRY_URL, or auto-discovers it over mDNS (_nmos-query._tcp).
• Security-first — a permission policy is enforced inside the server so an AI agent gets exactly the access it should have, and no more (see Permissions).

Designed with security in mind. This server exists to let an AI agent operate a live broadcast network, where a wrong connect can take a service to air or off it. Authorization is therefore enforced in code, before any request leaves the server — never as a system-prompt guideline the model could ignore or be talked out of. You grant an agent the minimum it needs (read-only, or writes limited to specific devices/groups); everything else is denied by default.

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Two ways to run it

	Option A — Local (Python venv)	Option B — Docker
Setup	pip install -e . in a venv	docker build -t nmos-mcp .
Best for	A laptop on the same network/VPN as the NMOS registry	Linux hosts / servers, or reproducible/isolated deployments
Networking	Uses the host's DNS, routes and VPN directly — simplest	The container must be able to reach the registry and each Node's IS-05 endpoint (see the caveats in the Docker section)
mDNS discovery	Works	Only with --network host on Linux

Steps 1–4 below cover Option A. The Docker path is in Run with Docker. Both are configured with the same NMOS_* environment variables (see Configure).

On a corporate laptop where the NMOS network is reachable only over VPN, Option A is usually the least friction — containers don't inherit the host's VPN DNS/routes by default. Use Docker where the registry and nodes are directly reachable from containers (e.g. a Linux box on the media network).

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1. Install

cd nmos-mcp
python3 -m venv .venv
source .venv/bin/activate
pip install -e ".[dev]"          # or: uv pip install -e ".[dev]"

This creates the nmos-mcp console command inside .venv/bin/.

Note (this machine): the shell auto-activates another project's virtualenv, so plain python3 may be the wrong interpreter. If python3 -m venv fails, build the venv with the real interpreter: env -i HOME="$HOME" PATH="/usr/bin:/bin" /opt/homebrew/bin/python3 -m venv .venv and use .venv/bin/python / .venv/bin/nmos-mcp directly.

2. Configure

Copy .env.example to .env and point it at your registry:

cp .env.example .env

NMOS_REGISTRY_URL=http://registry.example.local   # leave UNSET to auto-discover via mDNS
NMOS_QUERY_VERSION=v1.3
NMOS_CONNECTION_VERSION=v1.1
NMOS_USE_HTTPS=false
NMOS_VERIFY_TLS=true
# Permissions (optional; see the Permissions section below):
# NMOS_PERMISSIONS_FILE=permissions.yaml
# NMOS_PERMISSIONS_MODE=enforce            # 'open' disables all checks (dev only)
# IS-10 auth (optional, for secured deployments):
# NMOS_AUTH_ENABLED=true
# NMOS_AUTH_TOKEN_URL=https://auth.local/oauth2/token
# NMOS_AUTH_CLIENT_ID=...
# NMOS_AUTH_CLIENT_SECRET=...

.env is git-ignored — internal hostnames (e.g. registry.example.local) and credentials never get committed. .env.example is the only env file in git.

.env is read relative to the process working directory. When Claude Code launches the server the working directory may differ, so pass the registry URL via -e in the Claude Code registration below (that value is stored in your private Claude config, not in the repo).

3. Start the server

The server speaks the MCP protocol over a transport — you normally don't run it by hand; an MCP client (Claude Code) launches it. To run it manually:

nmos-mcp            # stdio transport (what Claude Code / Claude Desktop use)
nmos-mcp --http     # streamable-HTTP transport

To poke at the tools interactively with the MCP Inspector:

mcp dev src/nmos_mcp/server.py

4. Add it to Claude Code

Register the server with the CLI (from anywhere). Use -e to inject the registry URL and -s local so it stays in your private config rather than the shared repo:

claude mcp add nmos \
  -s local \
  -e NMOS_REGISTRY_URL=http://registry.example.local \
  -- /ABSOLUTE/PATH/TO/nmos-mcp/.venv/bin/nmos-mcp

Verify it connected:

claude mcp get nmos       # Status: ✔ Connected
claude mcp list

Then in a Claude Code session just ask, e.g.:

"List the NMOS senders, then connect 'AES67 sender 4' to 'AES67 receiver 4'."

To update or remove it:

claude mcp remove nmos -s local          # then re-add with new flags

Scopes: -s local (default) keeps the server private to you for this project (stored in ~/.claude.json). -s user makes it available in all your projects. Avoid -s project (writes a committed .mcp.json) unless you deliberately want the registry URL shared with the team via git.

Claude Desktop (alternative client)

Add to claude_desktop_config.json:

{
  "mcpServers": {
    "nmos": {
      "command": "/ABSOLUTE/PATH/TO/nmos-mcp/.venv/bin/nmos-mcp",
      "env": { "NMOS_REGISTRY_URL": "http://registry.example.local" }
    }
  }
}

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Run with Docker (Option B)

Build the image:

docker build -t nmos-mcp .

The image runs the stdio server by default and takes the same NMOS_* environment variables. .env and policy files are not baked in (see .dockerignore) — pass configuration at runtime.

Register the containerised server with Claude Code (note docker run -i — the -i keeps stdin open for the MCP stdio protocol):

claude mcp add nmos -s user -- \
  docker run -i --rm \
    -e NMOS_REGISTRY_URL=http://registry.example.local \
    -e NMOS_PERMISSIONS_MODE=open \
    nmos-mcp

Streamable-HTTP instead of stdio (long-running, exposes a port). Set NMOS_HTTP_HOST=0.0.0.0 so the server binds all interfaces and the published port is reachable (it defaults to 127.0.0.1):

docker run --rm -p 8000:8000 \
  -e NMOS_REGISTRY_URL=http://registry.example.local \
  -e NMOS_HTTP_HOST=0.0.0.0 \
  nmos-mcp --http
# clients connect to http://localhost:8000/mcp

With Docker Compose — a long-running HTTP service (binds 0.0.0.0, publishes 8000, restarts, health-checked); reads NMOS_* from your git-ignored .env:

docker compose up -d --build      # start
docker compose logs -f            # follow
docker compose down               # stop

Register the HTTP endpoint with Claude Code:

claude mcp add nmos-http -s user --transport http http://localhost:8000/mcp

A permission policy is mounted at runtime rather than built in:

docker run -i --rm \
  -e NMOS_REGISTRY_URL=http://registry.example.local \
  -e NMOS_PERMISSIONS_FILE=/policy.yaml \
  -v "$(pwd)/permissions.yaml:/policy.yaml:ro" \
  nmos-mcp

Networking — the important caveat

The container must be able to reach both the registry and every Node's IS-05 endpoint (often raw 192.168.x addresses on the media LAN).

• Linux host: add --network host so the container resolves names and routes exactly like the host. This is also the only way mDNS auto-discovery works in a container.
• Docker Desktop (macOS/Windows): --network host maps to Docker's Linux VM, not your machine, so corporate/VPN DNS names may not resolve and VPN-only subnets may be unroutable. Work around it by pointing NMOS_REGISTRY_URL at an IP, adding --add-host registry.example.local:<ip>, or --dns <corporate-dns> --dns-search <your.domain>. mDNS discovery does not work here. If the NMOS network is only reachable over the host's VPN, prefer Option A.

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Tools

IS-04 (query): registry_info, list_nodes, list_devices, list_senders, list_receivers, list_flows, list_sources, get_resource, query_resources.

IS-05 (connection): get_sender, get_receiver, get_sender_transport_file, connect_sender_to_receiver, disconnect_receiver, enable_sender, disable_sender, bulk_connect, stage_receiver, stage_sender.

Visualisation: crosspoint_matrix (read-only — router-style grid of all routes).

Permissions: permissions_info (read-only — shows the active policy).

Crosspoint matrix

A broadcast-router-style overview of every connection at once: senders are columns, receivers are rows, and a cell shows X where a receiver is subscribed to a sender (o = subscribed but inactive, . = not connected), with legends mapping the S1/R1 codes to labels and IDs. It's built from the receivers' IS-04 subscription data — one registry query, no per-Node calls.

Two ways to view it:

• From the terminal — the nmos-crosspoint CLI (installed alongside nmos-mcp):

  nmos-crosspoint              # colourised when the output is a TTY
  nmos-crosspoint --no-color
  

• From an agent — ask Claude to call the crosspoint_matrix tool ("show me the crosspoint matrix").

                         │ S1  S2  S3  S4  S5  S6  S7  S8  S9  S10
─────────────────────────┼────────────────────────────────────────
R5 AES67 receiver 3      │ .   .   .   .   .   X   .   .   .   .
R6 AES67 receiver 4      │ .   .   .   .   .   .   X   .   .   .

How a connection is made

The Query API lives on the registry; the Connection API (IS-05) lives on each Node. To wire a sender to a receiver the server:

1. Looks the receiver up in the registry and reads its device's controls array to find the IS-05 endpoint (urn:x-nmos:control:sr-ctrl).
2. Fetches the sender's SDP transport file.
3. PATCHes the receiver's /staged with the sender id, master_enable: true, the transport file, and activation: { mode: activate_immediate }.
4. Reads back the receiver's /active state to confirm the route.

The connection endpoint version is taken from the device's advertised control href, so nodes exposing IS-05 v1.0 or v1.1 both work.

Permissions (MCP-enforced authorization)

This is the server's core security mechanism: give an AI agent just the access it should have. Write actions can route real media, so the server enforces an authorization policy in code, before any HTTP call — it is not a system-prompt guideline and cannot be talked around by the LLM. Scope an agent down to read-only, or to writes on a single studio/rack, and everything else is denied by default.

Posture:

• Reads/queries are always allowed (discovery is never blocked).
• Every write action must be explicitly granted by a rule whose scope matches the target. Actions: connect, disconnect, enable, disable, stage (write = all five). Anything not granted is denied; explicit deny rules override allows.
• connect/disconnect/stage on a receiver are checked against the receiver; enable/disable/stage on a sender are checked against the sender.

Enable it by pointing at a policy file:

NMOS_PERMISSIONS_FILE=permissions.yaml     # YAML or JSON
NMOS_PERMISSIONS_MODE=enforce              # 'open' bypasses all checks (dev/testing)

In enforce mode with no file, all write actions are denied. Copy permissions.example.yaml to start. One policy applies per running server; give someone a different role by registering a second MCP server with its own policy and NMOS_PERMISSIONS_FILE.

Groups of devices can be defined by NMOS tags, explicit device UUIDs, label regex, or by Node (a resource matches if any selector matches the resource or its owning device). Minimal example — allow routing only onto the AES67 receivers:

groups:
  aes67_rx:
    labels: ["^AES67 receiver"]
rules:
  - actions: [connect, disconnect]
    groups: [aes67_rx]

Ask the agent to call permissions_info to see exactly what the running server will allow. Every write decision is written to stderr as an AUDIT ALLOW/DENY line. See permissions.example.yaml for tags/UUID/node examples and deny rules.

Test

pytest

Unit tests mock both the Registry Query API and a Node Connection API (via respx), covering the connect/disconnect PATCH bodies, endpoint resolution, config coercion and URL handling.

End-to-end against a real registry

Point NMOS_REGISTRY_URL at a live registry (or a local EasyNMOS stack: docker run -d --net=host rhastie/easy-nmos), then use mcp dev or Claude Code to list_senders / list_receivers, run connect_sender_to_receiver, and confirm the receiver's /active shows the sender's multicast group.

Scope & roadmap

Current: IS-04 read/query + IS-05 connection management. The module layout leaves room to add IS-04 registration writes, IS-08 audio channel mapping, IS-07 events/tally and IS-09 system parameters as additional tool groups.