OPC UA MCP Server (Node)

A Node / TypeScript Model Context Protocol (MCP) server for OPC UA operations, runnable with npx. It lets an MCP client read and write nodes, browse an address space, call methods, watch nodes for changes, and work the alarm and history surfaces of an OPC UA server.

There is a Python runtime exposing the same tools from the same contract. Both are first-class: one test suite runs against both, and they are released together under one version. Pick whichever stack you already run; the few declared differences between them, and the known divergences still being fixed, are listed in docs/compatibility.md.

Features

• Read nodes — value, data type, status, timestamps, and the engineering unit and range the node publishes, so a 51.75 arrives labelled °C rather than bare
• Write nodes — with the value bounded by the node's own published EURange before anything is sent, on top of whatever your policy allows
• Browse — list children, walk a subtree, resolve a browse path or search by name, with each node's HasTypeDefinition so an alarm reads as an alarm rather than as Object
• Call methods on object nodes
• Data-change subscriptions — watch nodes instead of polling them, with an optional absolute or percent deadband so jitter is discarded at the server
• Events and alarms — collect events from a notifier node, list the alarms the server retains, and acknowledge, confirm, annotate or shelve them
• History — historical values, raw or summarised by a server-side aggregate, and events the server stored for a range that has already passed
• Server health — connection state, the namespace array, and the OPC UA server's own ServerDiagnosticsSummary counters
• Tool profiles and an audit trail — an observe-only default, an allowlist for control, and every control call recorded
• Reconnection — a dropped session is rebuilt with backoff and the subscriptions on it re-created

Installation & Usage

Using npx (Recommended)

You can run the server directly using npx without installing it globally:

npx opcua-mcp-server

Global Installation

npm install -g opcua-mcp-server
opcua-mcp-server

Registering with Claude Desktop or Codex

Rather than editing claude_desktop_config.json (or Codex's config.toml) by hand, let the server write it:

opcua-mcp-server --install claude-desktop --dry-run \
  --url opc.tcp://192.168.0.10:4840 \
  --security-policy Basic256Sha256 \
  --client-cert /etc/opcua/client.pem --client-key /etc/opcua/client_key.pem \
  --server-cert /etc/opcua/server.pem

--dry-run validates the files and the combination with the server's own startup parsers and prints a redacted preview and a security summary; drop it to write (--install codex for Codex). It merges into the existing config, backs the old one up, and records absolute paths — Claude Desktop is launched from the GUI and does not inherit a login shell's PATH, so a bare "command": "npx" often works in a terminal and fails in the app. The profile defaults to read-only; a control profile must be chosen with --profile, and for a remote endpoint needs a pinned --server-cert. Passwords are never accepted as flags. --force replaces an existing opcua entry. Every flag and rule is in docs/install.md.

There is also a downloadable .mcpb bundle for Claude Desktop and single-file executables that need no Node at all — see docs/install.md.

Local Development

git clone <repository>
cd packages/server-node
npm install
npm run build
npm start

Tools

Both runtimes expose the same 15 tools — 7 read, 4 monitor, 2 alarm-action and 2 control — defined once in contract/tools.json.

| Tool | Access | Hints | What it does | | ------------------------- | ------------ | ----------------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | read_opcua_nodes | read | read-only, idempotent | Read the current value of one or more OPC UA nodes in a single request. | | browse_opcua_nodes | read | read-only, idempotent | Explore the OPC UA address space: list a node's children, walk a subtree, resolve a human-readable browse path to a node ID, or search for nodes by name. | | read_opcua_history † | read | read-only, idempotent | Read what a node's value has been over time. | | read_event_history † | read | read-only, idempotent | Read events the OPC UA server stored, for a time range that has already passed. | | get_server_status | read | read-only, idempotent | Report whether this MCP server is connected to the OPC UA server and what that server says about itself: its endpoint and connection security, its ServerStatus (state, current time, start time, build info) and its NamespaceArray as index -> URI. | | list_subscriptions | read | read-only, idempotent | List the active OPC UA data-change subscriptions, each with the value changes buffered for it since it was created. | | list_active_alarms | read | read-only, idempotent | List the alarm and condition instances the server is currently retaining — those that are active, unacknowledged, or both. | | subscribe_opcua_nodes | monitor | — | Watch one or more OPC UA nodes for value changes instead of polling them. | | unsubscribe_opcua_nodes | monitor | — | Cancel one or more active data-change subscriptions and discard what they had buffered. | | subscribe_events | monitor | — | Start buffering OPC UA events (alarms, condition changes, plain events) from a notifier node. | | read_events | monitor | — | Read the events buffered by subscribe_events, oldest first. | | acknowledge_alarm | alarm-action | — | Acknowledge an alarm or condition, identified by the event_id of the event that reported it (from list_active_alarms or read_events). | | act_on_alarm | alarm-action | — | Confirm, annotate or shelve an alarm — the rest of the operator workflow that acknowledge_alarm starts. | | write_opcua_nodes | control | destructive, idempotent | Write a value to one or more OPC UA nodes. | | call_opcua_method | control | destructive | Call a method on an OPC UA object. |

Access decides which OPCUA_PROFILE offers a tool. read and monitor tools are offered under every profile, including the default observe. control tools need operator, which offers them only for allowlisted targets, or full; alarm-action tools need operator with OPCUA_ALLOW_ACKNOWLEDGE_ALARMS, or full. Both also need a verified server — a secured channel and an authenticated server, pinned with OPCUA_SERVER_CERT or validated by OPCUA_SERVER_TRUST_STORE — unless a lab override is set: OPCUA_ALLOW_INSECURE_CONTROL for a channel with no security, OPCUA_ALLOW_UNVERIFIED_SERVER_CONTROL for an unauthenticated server. Hints are the MCP tool annotations each tool advertises.

† Needs a server feature: always listed, and refused at call time with capability_not_supported or capability_unknown when the connected server does not advertise what it needs — read_opcua_history on AccessHistoryDataCapability or AggregateFunctions; read_event_history on AccessHistoryEventsCapability.

read_opcua_history needs historical access (AccessHistoryDataCapability) or aggregates (a non-empty AggregateFunctions folder), and its aggregate_function argument needs the latter. read_event_history needs AccessHistoryEventsCapability — keeping values and keeping events are different features and a server commonly does one without the other. Every tool is listed whatever the plant is doing, with the same schema, because MCP clients keep the first list they get and nothing tells them reliably to ask again. A call the connected server cannot serve is refused before anything is sent, with a code to act on — capability_not_supported, capability_unknown, or endpoint_offline when the server cannot be reached — and what to use instead. get_server_status → capabilities reports what the server was found to offer, including its aggregate function names, on which session and when.

One tool per operation, not one per arity. Reading one node and reading fifty is the same request with a longer list, so it is one tool and one code path.

Bounded, and honest about it. Every request is bounded before it reaches the OPC UA server — at most 500 nodes per read, 100 per write, 64 method arguments, 1 MiB of arguments, and fewer where the OPC UA server publishes lower OperationLimits; the full list is in the tools reference. A request over a bound is refused whole, never partly sent. And every result that can be partial — history, events, browse, subscriptions — carries a completeness object beside result in structuredContent: test completeness.complete, and never infer it from how many records came back.

Full per-tool reference with inputs, outputs and a node-ID map: docs/examples.md.

Resources

One resource, opcua://subscriptions: the active data-change subscriptions and the values each has buffered, as JSON. It is the same set of records list_subscriptions returns, re-readable without spending a tool call. See Subscriptions for the shape and the worked example.

Configuration

The server is configured entirely through environment variables. Every one is declared, with its type, default and secrecy, in the repository's contract/config.json, which both runtimes are tested against and which ships inside this package:

31 settings in six groups. A blank value means the default, whatever the type; a boolean accepts 1, true, yes, on and 0, false, no, off.

Connection — Which OPC UA server to talk to.

| Variable | Default | Description | | ------------------ | -------------------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | OPCUA_SERVER_URL | opc.tcp://localhost:4840 | URL of the OPC UA server to connect to, including any path the server expects. Read once at startup: one process serves one endpoint. Verify who answers with an exact server certificate pin or a configured CA trust store. |

Channel security — How the OPC UA secure channel is signed, encrypted and verified.

| Variable | Default | Description | | ------------------------------ | ------------------------------------------------------------ | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | OPCUA_SECURITY_POLICY | None | Encryption suite to negotiate for the secure channel. Anything other than None needs a client certificate and key. The two AES suites are Node-only: the Python runtime refuses them at startup rather than downgrading. One of None, Basic128Rsa15, Basic256, Basic256Sha256, Aes128_Sha256_RsaOaep, Aes256_Sha256_RsaPss. None is unencrypted and unauthenticated, and keeps control tools blocked unless insecure control is explicitly allowed. An unknown policy stops the server at startup. | | OPCUA_SECURITY_MODE | SignAndEncrypt once a security policy is set, otherwise None | Message security mode for the secure channel. Sign authenticates messages without encrypting them. One of None, Sign, SignAndEncrypt. A policy with mode None, or a mode without a policy, stops the server at startup; leaving it blank never downgrades a policy to signing only. | | OPCUA_CLIENT_CERT | — | Path to the certificate (PEM or DER) this client presents as its application identity. Required by any security policy other than None. A path that does not exist stops the server at startup. | | OPCUA_CLIENT_KEY | — | Path to the private key matching the client certificate. A path, never key material. Whoever can read the file can impersonate this client: keep it readable only by the account running the server. A path that does not exist stops the server at startup. | | OPCUA_APPLICATION_URI | the subjectAltName URI of the client certificate | Application URI announced to the server. Set it only for a certificate that carries no URI of its own. A configured URI that conflicts with the certificate is refused before connecting. | | OPCUA_SERVER_CERT | — | Path to the OPC UA server's own certificate (PEM or DER), pinned: a server presenting any other certificate cannot complete the handshake. Control tools (writes, method calls, alarm actions) require it, or OPCUA_SERVER_TRUST_STORE instead. Requires a security policy other than None. Unset, encryption protects against eavesdropping but not against an impostor endpoint, so control tools are refused unless OPCUA_SERVER_TRUST_STORE validates the server or OPCUA_ALLOW_UNVERIFIED_SERVER_CONTROL is set. Set without a security policy, it stops the server at startup rather than pinning nothing; a pinned certificate that has expired or is not yet valid refuses to connect. | | OPCUA_SERVER_TRUST_STORE | — | Directory with trusted/certs root CAs, issuers/certs intermediate CAs, and trusted/crl plus issuers/crl signed current revocation lists. Authenticate the OPC UA peer by its validated chain and expected server URI. Requires secured channel and OPCUA_SERVER_APPLICATION_URI; Python requires the maintained asyncua backend. Missing, stale, forged or revoked trust material refuses connection. Cannot be combined with an exact server certificate pin. | | OPCUA_SERVER_APPLICATION_URI | — | ApplicationUri of the intended OPC UA server. Must match the peer certificate URI SAN and advertised application identity. Required with OPCUA_SERVER_TRUST_STORE. |

User identity — Who the OPC UA session logs in as.

| Variable | Default | Description | | ----------------- | ------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ | | OPCUA_USERNAME | — | OPC UA username. The session is anonymous when unset. Cannot be combined with a user certificate. Requires a password; either one alone stops the server at startup. | | OPCUA_PASSWORD | — | Secret. Password for the username. Without a security policy it crosses the network in clear text. Supply it through the client's secret storage, never on a command line. | | OPCUA_USER_CERT | — | Path to the certificate identifying the user, for X.509 user authentication: a different key pair from the client certificate, which secures the channel. Requires the user key and a security policy other than None; cannot be combined with a username. Any of those combinations broken stops the server at startup. | | OPCUA_USER_KEY | — | Path to the private key for the user certificate. It signs the server's challenge and is never sent. Whoever can read the file can log in as this user: keep it readable only by the account running the server. |

Tool policy — Which MCP tools are offered, and what a control tool may touch.

| Variable | Default | Description | | --------------------------------------- | --------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | OPCUA_PROFILE | observe | Which tools are offered. observe reads, browses, reads history and monitors; operator adds explicitly allowlisted writes, method calls and alarm actions; full exposes every tool and is meant only for a tightly scoped OPC UA account. One of observe, operator, full (read-only means observe; readonly means observe). Unset fails closed to observe; an unknown profile stops the server at startup. | | OPCUA_POLICY_FILE | — | Path to a version-1 JSON policy file, the only place per-node value bounds, writable_subtrees, preconditions, the alarm scope and deny_read can be set. Every policy variable that is set overrides what the file says. An unreadable or invalid file stops the server at startup. | | OPCUA_ALLOWED_TOOLS | — | Comma-separated tool allowlist. It can only narrow the selected profile, never widen it. An unknown tool name stops the server at startup. | | OPCUA_ALLOWED_WRITE_NODES | — | Comma-separated exact node IDs the operator profile may write, as ns=2;i=5 or, stable across a server restart, nsu=<namespace-uri>;i=5 or a browse path from the Root folder such as /Objects/Line1/Setpoint. Setting it replaces the policy file's list, bounds included. Empty fails closed: operator can write nothing. A batch write with any target outside the list is refused before it reaches OPC UA. | | OPCUA_ALLOWED_METHODS | — | Comma-separated object_node_id|method_node_id pairs the operator profile may call. Either half may be a browse path from the Root folder. Empty fails closed: operator can call nothing. An entry without | stops the server at startup. | | OPCUA_ALLOW_ACKNOWLEDGE_ALARMS | false | Let the operator profile act on alarms: acknowledge_alarm and every act_on_alarm action. | | OPCUA_ALLOW_INSECURE_CONTROL | false | Permit control tools on an OPC UA channel with no security policy (None). Does not cover a secured channel to an unverified server; that is OPCUA_ALLOW_UNVERIFIED_SERVER_CONTROL. Fail-open override: writes, method calls and alarm actions then travel unauthenticated and unencrypted. Reported as control=INSECURE-OVERRIDE in the startup line, get_server_status and every audit record. Never enable it against production equipment. | | OPCUA_ALLOW_UNVERIFIED_SERVER_CONTROL | false | Permit control tools on a secured OPC UA channel whose server is not authenticated: neither pinned with OPCUA_SERVER_CERT nor validated by OPCUA_SERVER_TRUST_STORE. Does not cover a channel with no security policy; that is OPCUA_ALLOW_INSECURE_CONTROL. Fail-open override: writes, method calls and alarm actions are then encrypted to whichever server answered the endpoint, which may be an impostor. Reported as control=UNVERIFIED-OVERRIDE in the startup line, get_server_status and every audit record. Never enable it against production equipment. | | OPCUA_ALLOW_OUT_OF_RANGE_WRITES | false | Allow a write outside the EURange the OPC UA server itself published for the node. A published InstrumentRange still applies. Fail-open override: it discards the only value bound a deployment with no policy file has. |

Audit — Where the control audit trail goes, and what it is labelled with.

| Variable | Default | Description | | ---------------------------- | -------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | OPCUA_AUDIT_FILE | — | Path to an append-only file for the control audit trail, one JSON object per line, written beside stderr. Created owner-only (0600) if it does not exist; reopened when rotated away. A file that cannot be opened, or that is a symlink, not a regular file, another account's, or group/world-writable, stops the server rather than falling back to stderr alone. While set, a control call whose record cannot be written is refused (fail closed); reads continue. | | OPCUA_AUDIT_FSYNC | always | When an audit-file record counts as written. always fsyncs each record before the control call proceeds, so it survives a power loss; none leaves it to the operating system, so it survives only a crash of this process. One of always, none. none can lose the records of control calls that already reached the plant if the machine loses power. | | OPCUA_AUDIT_CHAIN | none | Adds seq, prev_hash and hash to every audit record so edits, deletions and reordering can be detected with --verify-audit. sha256 catches accidental or naive edits; hmac-sha256 also resists anyone without the key. Requires the audit file. One of none, sha256, hmac-sha256. Set without an audit file, or hmac-sha256 without a key file, stops the server. No chain detects a truncated tail. | | OPCUA_AUDIT_CHAIN_KEY_FILE | — | Path to the HMAC key for the hmac-sha256 audit chain: at least 32 bytes, for example from openssl rand -hex 32. Surrounding whitespace is ignored. Whoever can read the key can forge the chain: a key readable or writable by group or others stops the server. Refused unless the chain is hmac-sha256. | | OPCUA_OPERATOR_ID | — | Label stamped on every audit record as operator_label, so a shipped log says which deployment a control call came from. Configured, never verified: it is not an identity, and mcp_principal stays null. |

Reconnection — How a refused or dropped connection is retried.

| Variable | Default | Description | | ---------------------------------- | ------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ | | OPCUA_RECONNECT_INITIAL_DELAY_MS | 1000 | Wait before the first attempt to repair a dropped or refused connection, in milliseconds. It doubles with each further attempt. | | OPCUA_RECONNECT_MAX_DELAY_MS | 8000 | Ceiling for the doubling retry delay, in milliseconds. | | OPCUA_RECONNECT_MAX_RETRY | 3 | Retries after the first attempt, per connection round, before a tool call gives up: a whole number from -1 to 1000. 0 never retries; -1 never stops trying, in bounded rounds of four retries so no single call waits forever. | | OPCUA_SESSION_TIMEOUT_MS | 60000 | Session lifetime asked of the OPC UA server, in milliseconds. It also sets the keep-alive period, so it decides how quickly an idle connection notices the server has gone. |

Names are case-insensitive, and a policy on its own implies SignAndEncrypt. An unusable combination — a mode without a policy, a policy without a certificate, a username without a password — is refused at startup with a message naming the variable. With no security configured the connection is unencrypted and unauthenticated, and the server says so on stderr; see SECURITY.md. Making a client certificate and getting it trusted: docs/certificates.md.

Examples:

# unsecured, e.g. against the bundled mock
OPCUA_SERVER_URL=opc.tcp://192.168.1.100:4840 npx opcua-mcp-server

# encrypted and authenticated
OPCUA_SERVER_URL=opc.tcp://plc.example.internal:4840 \
OPCUA_SECURITY_POLICY=Basic256Sha256 \
OPCUA_CLIENT_CERT=/etc/opcua/client.pem \
OPCUA_CLIENT_KEY=/etc/opcua/client_key.pem \
OPCUA_SERVER_CERT=/etc/opcua/plc_server.pem \
OPCUA_USERNAME=mcp-operator OPCUA_PASSWORD=… \
  npx opcua-mcp-server

Deciding what the agent may do

Three profiles, and the default is the restrictive one:

| OPCUA_PROFILE | What it offers | | --------------------- | -------------------------------------------------------------------- | | observe (default) | Read, browse, history and monitoring. No writes, no methods | | operator | The above, plus only the write targets and methods you allowlist | | full | Every tool |

operator is the one worth understanding. A write to a node outside OPCUA_ALLOWED_WRITE_NODES is refused before anything reaches OPC UA, and one forbidden target rejects an entire batch rather than letting part of it through. Both operator and full also require a verified server: a security policy and an authenticated server — its certificate pinned with OPCUA_SERVER_CERT, or validated against a CA trust store with OPCUA_SERVER_TRUST_STORE + OPCUA_SERVER_APPLICATION_URI. Encrypted is not enough — without either the channel is encrypted to whoever answered. Two lab-only overrides say otherwise in as many words, one per missing property: OPCUA_ALLOW_INSECURE_CONTROL=true for a channel with no security, and OPCUA_ALLOW_UNVERIFIED_SERVER_CONTROL=true for a secured one to an unauthenticated server. A refused control call names the variable to set, and get_server_status → server_identity says which of the three is in force.

The policy is enforced again on every call, not only when tools are listed — an MCP client may hold a stale catalogue, and a hidden tool is a usability feature rather than a security boundary.

A writable_nodes entry in a policy file may also bound the value, not only the node: min, max, enum and max_change narrow what an allowlisted node will accept, so a model that picks the right node and hallucinates 9999 instead of 99.9 is refused. The node's own published EURange applies on top, which is the only value bound that exists with no policy file at all. See Bounding the value, not only the node.

Every control call is recorded — its targets, its outcome, the endpoint it went to, the session it rode on and the attempt number — to stderr and, with OPCUA_AUDIT_FILE set, to an owner-only, append-only JSON-lines file beside it, fsync'd per record by default. A control call whose record cannot be written is refused rather than sent; reads carry on. OPCUA_AUDIT_CHAIN adds an optional hash chain, checked with opcua-mcp-server --verify-audit FILE… [--key-file KEY]. What the file can and cannot prove is in SECURITY.md.

Staying connected

The connection is re-established by itself: a dropped or refused session is retried with exponential backoff, and the read and write paths rebuild a dead session rather than failing until the process is restarted. Data-change subscriptions are re-created on the new session — the IDs keep working and the values already buffered are still there to be read. Event subscriptions are re-created too, and the next read_events notes that events raised while the connection was down were not received. Tune it with OPCUA_RECONNECT_INITIAL_DELAY_MS, OPCUA_RECONNECT_MAX_DELAY_MS, OPCUA_RECONNECT_MAX_RETRY and OPCUA_SESSION_TIMEOUT_MS above.

The MCP server starts whether or not the OPC UA server is reachable: it answers initialize at once and makes its first connection in the background, so an endpoint that is down — even with OPCUA_RECONNECT_MAX_RETRY=-1 — is reported rather than leaving the MCP client waiting on a server that never starts.

get_server_status reports whether the connection is up and what the OPC UA server says about itself; it is the one tool that answers while the connection is down, and calling it is also what brings a dropped one back. See Staying connected.

A control call whose session died before its response arrived is not silently re-sent. OPC UA lets a Write partially succeed and defines no operation order, so a dead session never proves the write did not land: the server rebuilds the connection and then says plainly that the request may or may not have reached the plant, naming what it was aimed at.

Integration with Cursor/Claude

This server can be integrated with Cursor IDE or Claude Desktop for OPC UA operations. Add the following to your MCP configuration:

Cursor Configuration

Add to your Cursor settings:

{
  "mcpServers": {
    "opcua-node": {
      "command": "npx",
      "args": ["opcua-mcp-server"],
      "env": {
        "OPCUA_SERVER_URL": "opc.tcp://localhost:4840"
      }
    }
  }
}

Claude Desktop Configuration

Add to your Claude Desktop configuration file:

{
  "mcpServers": {
    "opcua-node": {
      "command": "npx",
      "args": ["opcua-mcp-server"],
      "env": {
        "OPCUA_SERVER_URL": "opc.tcp://localhost:4840"
      }
    }
  }
}

Example Usage in Conversation

Once configured, you can ask Claude to perform real-world OPC UA operations:

Reading Sensor Values

• "What is the current temperature reading from the reactor vessel?"
• "Check the pressure level in Tank A"
• "Read all temperature sensors in the cooling system"
• "Get the current flow rate on production line B"

Controlling Equipment

• "Turn on the conveyor motor"
• "Set the mixer speed to 80 RPM"
• "Open valve V-101 to 75% position"
• "Start the circulation pump"
• "Set the heating element to 150°C"

Alarms

• "What alarms are active right now?"
• "Acknowledge the high-temperature alarm with a note about the cause"
• "Shelve that chattering level alarm for thirty minutes"
• "What fired overnight on the packaging line?"

System Monitoring

• "Read all sensor values from the water treatment plant"
• "Check the status of all pumps and motors"
• "Is the plant server refusing our connections, or just slow?"
• "Watch the reactor temperature and ignore changes under 0.5°C"
• "Show me a complete inventory of all sensors and actuators"

Real Example Scenarios

User: "What's the temperature in reactor R-101?"
Assistant: I'll read the temperature sensor for reactor R-101.
Tool call: read_opcua_nodes with node_ids ["ns=2;i=11"]
Result: "Reactor R-101 temperature: 87.3 °C (range 0–150 °C)"

User: "Turn on the main conveyor motor"
Assistant: I'll start the main conveyor motor for you.
Tool call: write_opcua_nodes with nodes [{node_id: "ns=2;i=12", value: true}]
Result: "Main conveyor motor started successfully"

User: "Set the pump speed to 65%"
Assistant: I'll adjust the pump speed to 65%.
Tool call: write_opcua_nodes with nodes [{node_id: "ns=2;i=13", value: 65}]
Result: "Pump speed set to 65%"

User: "Show me all available variables in the system"
Assistant: I'll browse the OPC UA server's address space.
Tool call: browse_opcua_nodes
Result: "Found 15 variables:
- Name: Temperature_Sensor_01, NodeID: ns=2;i=101, Type: AnalogItemType, Value: 87.3 °C
- Name: Pressure_Sensor_01, NodeID: ns=2;i=102, Type: AnalogItemType, Value: 2.5 bar
- Name: Flow_Rate_01, NodeID: ns=2;i=103, Type: AnalogItemType, Value: 125.8 L/min
..."

Security Considerations

• The connection defaults to no security (SecurityPolicy.None); set OPCUA_SECURITY_POLICY and credentials as shown under Configuration for anything beyond local development
• The tool profile defaults to observe-only. Writes and methods require OPCUA_PROFILE=operator and an explicit allowlist, over a channel to a verified server
• Pin the endpoint with OPCUA_SERVER_CERT, or validate it against a CA trust store with OPCUA_SERVER_TRUST_STORE + OPCUA_SERVER_APPLICATION_URI. Without either the server certificate is taken from the endpoint description and not checked against anything, so encryption protects against eavesdropping but not against an impostor endpoint — and control tools are refused unless OPCUA_ALLOW_UNVERIFIED_SERVER_CONTROL says otherwise, for a lab
• Ensure proper network security when connecting to industrial OPC UA servers
• Scope the OPC UA account you connect with to what the assistant should be able to do — the MCP policy is defense in depth, not a replacement for OPC UA authorization

See SECURITY.md for the full posture and what the servers do and do not verify.

Error Handling

The server provides detailed error messages for:

• Connection failures, distinguishing a refusal from an outage mid-request
• Invalid node IDs, and arguments a schema rejects — including misspelled optional ones, which are refused rather than silently ignored
• Type conversion errors
• Values outside a node's published range or a policy's bounds
• Method call failures
• Read/write operation errors

Dependencies

• @modelcontextprotocol/sdk: MCP SDK for Node.js
• node-opcua-client: OPC UA client library for Node.js (the client half of node-opcua; the server half is not needed here and is deliberately not a dependency)

Contributing

We welcome contributions to improve the OPC UA MCP Server!

Repository: https://github.com/IndustriAgents/OPCUA-MCP

To contribute:

1. Fork the repository at https://github.com/IndustriAgents/OPCUA-MCP
2. Create a feature branch (git checkout -b feature/amazing-feature)
3. Make your changes
4. Add tests if applicable
5. Commit your changes (git commit -m 'Add some amazing feature')
6. Push to the branch (git push origin feature/amazing-feature)
7. Open a Pull Request

Please feel free to open issues for bug reports, feature requests, or questions.

License

MIT License - see LICENSE file for details

Support

For issues and questions:

• Open an issue on GitHub
• Check the OPC UA server connectivity with get_server_status
• Verify node IDs are correct
• Ensure proper permissions for OPC UA operations
• Review server logs for detailed error information