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opcua-mcp

by mwieczorkiewicz
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OPC-UA MCP Server

An MCP server that lets an LLM read, write, browse, search, and subscribe to live data on an OPC-UA industrial automation server - over stdio or HTTP, with a persistent cache and a searchable index of the address space built in.

https://github.com/user-attachments/assets/0b676e6e-17ce-42f5-918f-9a615e939008

Quick start

The fastest way to see it working end-to-end, using the bundled Microsoft OPC-UA test server and a public tunnel Claude can reach:

git clone https://github.com/mwieczorkiewicz/opcua-mcp.git
cd opcua-mcp
make compose-up        # starts a test OPC-UA server, opcua-mcp, and a public HTTPS tunnel
make connector-url      # prints a URL like https://xyz.trycloudflare.com/mcp

Paste that URL into Claude at Settings → Connectors → Add custom connector, then ask it to browse the server or read a value. Stop with make compose-down when you're done - see docs/deployment.md for what that tunnel exposes and how to run against your own OPC-UA server instead.

Building and running locally

go build -o opcua-mcp ./cmd/opcua-mcp.go

# stdio (default) - no OPC-UA connection until the client calls opcua_connect
./opcua-mcp

# HTTP - connects eagerly at startup
SERVER_TRANSPORT=http OPCUA_ENDPOINT=opc.tcp://localhost:4840 ./opcua-mcp

Requires Go 1.26+ and, optionally, Docker for the test server / containerized deployment.

Related MCP server: OT-AIops

What it does

  • Read / write node values, with type validation on writes so a mismatched value is rejected before it reaches the device.

  • Browse the address space one level at a time or recursively, and look nodes up by name instead of by node ID.

  • Subscribe to push-based live updates - subscriptions persist across restarts and are automatically re-established on reconnect.

  • Cache reads, browse results, and type info on disk (bbolt), so repeat lookups don't round-trip to the device; writes invalidate the relevant entry automatically.

  • Discover and search the address space in the background, indexed with Bleve for fuzzy/partial browse-name lookups.

  • Anonymous, username/password, or certificate auth, with configurable OPC-UA security policy and mode.

See docs/architecture.md for how the caching layer, subscription manager, and discovery index fit together.

MCP tools

Tool

Description

opcua_read

Read one or more node values. Subscribed nodes are served from the live cache; others go live unless max_age_ms allows a cached value.

opcua_write

Write a value to a node. Validates the value's type against the node before writing.

opcua_get_value

Read a single node's value - a convenience wrapper over opcua_read.

opcua_get_value_by_name

Read a value by browse name instead of node ID, via the discovery index.

opcua_browse

List a node's immediate children.

opcua_browse_nodes

Recursively browse from a node up to a depth limit, nesting children under their parent.

opcua_node_info

Get a node's metadata (data type, access level, etc.).

opcua_find_similar_nodes

Fuzzy-match browse names against the discovery index.

opcua_subscribe

Start push-based updates for one or more nodes at a given interval.

opcua_unsubscribe

Cancel a subscription, by ID or by naming one of its nodes.

opcua_list_subscriptions

List active subscriptions.

opcua_connect / opcua_disconnect

Manage the connection explicitly (mainly relevant in stdio mode).

opcua_server_info

Get OPC-UA server metadata.

opcua_discovery_stats

Stats on the background discovery cache (node count, depth distribution, enabled flags).

opcua_force_discovery

Trigger an immediate discovery refresh instead of waiting for the next cycle.

opcua_debug_search / opcua_ensure_server_nodes

Diagnostics for troubleshooting why a node isn't showing up in search.

MCP resources

Resource

Description

opcua://node/{node_id}

Node data, e.g. opcua://node/ns=2;i=1. Accepts a comma-separated list for multiple nodes.

opcua://server

OPC-UA server information.

Configuration

Configuration is loaded (via viper) from three sources, in ascending order of precedence:

  1. Built-in defaults (shown in the tables below).

  2. An optional config file - TOML, YAML, JSON, or any other format viper supports. By default ./config.{yaml,yml,toml,json,...} is read if present; point at an explicit path with CONFIG_FILE=/path/to/config.toml. A config file is entirely optional - env vars alone are still enough.

  3. Environment variables (SERVER_*, OPCUA_*, MCP_*, SEARCH_*, STORE_*) - always win over the config file, so existing env-var-only deployments keep working unchanged.

A config file mirrors the env var names, lowercased and nested under each prefix, e.g. SERVER_HTTP_PORT becomes:

server:
  http_port: "8080"

Server

Variable

Default

Description

SERVER_TRANSPORT

stdio

stdio or http

SERVER_HTTP_PORT

8080

Port for HTTP transport

SERVER_LOG_LEVEL

info

debug, info, warn, error

SERVER_LOG_FORMAT

json

json or text

SERVER_LOG_OUTPUT

stdout

stdout, stderr, or file (forced to stderr in stdio mode, since stdout carries the MCP stream)

SERVER_LOG_FILE

-

Log file path, required if SERVER_LOG_OUTPUT=file

SERVER_LOG_ADD_SOURCE

false

Add source file/line to log entries

OPC-UA connection

Variable

Default

Description

OPCUA_ENDPOINT

opc.tcp://localhost:4840

Server endpoint

OPCUA_AUTH_MODE

anonymous

anonymous, username, or certificate

OPCUA_USERNAME / OPCUA_PASSWORD

-

Required if AUTH_MODE=username

OPCUA_CERT_FILE / OPCUA_KEY_FILE

-

Required if AUTH_MODE=certificate

OPCUA_SERVER_CERT

-

Server certificate file path

OPCUA_SECURITY_POLICY

None

None, Basic128Rsa15, Basic256, Basic256Sha256, Aes128_Sha256_RsaOaep

OPCUA_SECURITY_MODE

None

None, Sign, SignAndEncrypt

OPCUA_REQUEST_TIMEOUT

30s

Per-request timeout

OPCUA_SESSION_TIMEOUT

60s

Session timeout

OPCUA_MAX_RETRIES

3

Connection retry attempts

OPCUA_RETRY_DELAY

1s

Delay between retries

MCP

Variable

Default

Description

MCP_NAME

OPC-UA MCP Server

Server name reported to clients

MCP_VERSION

1.0.0

Server version reported to clients

MCP_ENABLE_TOOLS

true

Enable tools

MCP_ENABLE_RESOURCES

true

Enable resources

MCP_ENABLE_PROMPTS

false

Enable prompts

MCP_HTTP_PATH

/mcp

HTTP endpoint path

Discovery and search

Variable

Default

Description

SEARCH_ENABLE_DISCOVERY

true

Enable background node discovery

SEARCH_DISCOVERY_INTERVAL

30s

How often to re-crawl the address space

SEARCH_DISCOVERY_ROOT_NODE

i=85

Root node to crawl from (Objects folder)

SEARCH_MAX_DISCOVERY_DEPTH

10

Maximum crawl depth

SEARCH_MAX_NODES_PER_BROWSE

10000

Cap on nodes returned per browse call

SEARCH_ENABLE_SEARCH

true

Enable the Bleve search index

SEARCH_INDEX_PATH

./search_index

Search index directory

SEARCH_MAX_RESULTS

100

Max results per search

SEARCH_MIN_SCORE

0.1

Minimum match score

SEARCH_ENABLE_CACHE

true

Master switch for read-through caching. false makes every opcua_read/opcua_write/opcua_browse_nodes call go live, matching pre-cache behavior exactly

Persistent store

Backs read-through caching and subscription persistence with an on-disk bbolt database.

Variable

Default

Description

STORE_DB_PATH

mcp_opcua_store.db

Database file path

STORE_OPEN_TIMEOUT

5s

How long to wait for the file lock on open

STORE_TYPEINFO_TTL

24h

Freshness window for cached type info

STORE_BROWSE_TTL

5m

Freshness window for cached browse results

STORE_BATCH_WINDOW

25ms

How often subscription notifications flush to the store

STORE_BATCH_MAX_ITEMS

250

Max notifications flushed per batch

STORE_NOTIFY_CHAN_BUFFER

1024

Buffer size for incoming subscription notifications

If the store fails to open (e.g. a stale lock from a prior ungraceful shutdown, or a read-only filesystem), the server logs a warning and keeps running with caching forced off and subscription tools returning an error - every other tool is unaffected.

Telemetry

opcua-mcp collects anonymous, aggregate usage telemetry (which tools get used, cache hit rate, error categories - never node IDs, endpoint URLs, node values, or credentials) to help prioritize maintenance of this open-source project. It's on by default; see docs/telemetry.md for exactly what is and isn't collected.

Opt out with either:

Variable

Effect

DO_NOT_TRACK=1

The cross-project community convention (consoledonottrack.com)

OPCUA_MCP_TELEMETRY=false

This project's own switch

Docker

docker build -t opcua-mcp .
docker run -p 8080:8080 -e SERVER_TRANSPORT=http -e OPCUA_ENDPOINT=opc.tcp://your-server:4840 opcua-mcp

Multi-stage build on Chainguard's minimal Go image, running from scratch - no shell, small attack surface. Mount ./search_index and ./mcp_opcua_store.db as volumes to persist discovery/cache/subscription state across restarts. Full auth-mode examples, the Compose dev stack, and the Claude-connector tunnel setup are in docs/deployment.md.

Development

make start-opcua-server      # Microsoft OPC-UA test server in Docker
make run-with-test-server    # run the app against it (auto start/stop)

go test ./...                # unit tests
go test -race ./...
make test-integration        # real Subscribe/reconnect/cache behavior via testcontainers-go (needs Docker)

VS Code launch configs are in .vscode/launch.example.json - copy to .vscode/launch.json to get stdio/HTTP/auth debug targets that start and stop the test server automatically. make help lists every available target.

Tests are table-driven and mock the OPC-UA client at the opcuaClient interface seam (internal/opcua/mock_client_test.go) rather than against a live/simulated server - see docs/architecture.md for how the pieces being tested fit together, and docs/COMMIT_CONVENTION.md for this repo's commit message format.

Contributing

Fork it, make your changes, open a PR - see CONTRIBUTING.md.

License

MIT

This server cannot be installed

A
license - permissive license
-
quality - not tested
B
maintenance

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Maintenance

–Maintainers
<1hResponse time
–Release cycle
–Releases (12mo)
Commit activity

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