# OPC UA .NET Standard stack documentation
These guides lead from a first working application to advanced and experimental
capabilities. Follow the numbered stages when you are learning. Choose only the
paths that match your application, or use the contents list to find a feature.
- **New to the SDK?** Start with [Getting started](GettingStarted.md), read
[OPC UA concepts](Concepts.md), then build
[your first information model](FirstModel.md).
- **Upgrading from 1.5.x?** Read [What's New in 2.0](WhatsNewIn2.0.md), then
follow the [Migration Guide](MigrationGuide.md).
- **Contributing to this repository?** See
[Contributing and maintaining the SDK](#contributing-and-maintaining-the-sdk).
## Contents
- [How to use this index](#how-to-use-this-index)
- [1. Get started](#1-get-started)
- [2. Build your application](#2-build-your-application)
- [Client path](#client-path)
- [Server path](#server-path)
- [PubSub path](#pubsub-path)
- [3. Add data types and application services](#3-add-data-types-and-application-services)
- [Data types and models](#data-types-and-models)
- [Application services](#application-services)
- [4. Use companion models](#4-use-companion-models)
- [5. Prepare for production](#5-prepare-for-production)
- [6. Advanced integration, reliability, and scale](#6-advanced-integration-reliability-and-scale)
- [Transports and integration](#transports-and-integration)
- [Session recovery and performance](#session-recovery-and-performance)
- [Security infrastructure and fleet management](#security-infrastructure-and-fleet-management)
- [High availability and deployment](#high-availability-and-deployment)
- [Native AOT publishing](#native-aot-publishing)
- [7. Draft and experimental capabilities](#7-draft-and-experimental-capabilities)
- [Reference and upgrade](#reference-and-upgrade)
- [Contributing and maintaining the SDK](#contributing-and-maintaining-the-sdk)
## How to use this index
Each stage builds on the earlier ones, but you do not need to read every guide.
After stage 1, choose the client, server, or PubSub path. Stages 3 to 7 are
optional; use the guides your application needs. A stage or group names the
knowledge it assumes.
Labels describe the maturity of a package or model:
- **Preview package**: the package family keeps a `-preview` version, even when
the core packages are stable. See [Versioning](DeveloperGuide.md#versioning).
- **Draft model**: the guide implements a working-group draft specification.
Its namespace URIs and NodeIds are provisional.
- **Experimental**: the guide marks the feature as experimental.
These labels are independent of difficulty. An advanced guide can describe a
stable feature, and a released specification can ship in a preview package.
## 1. Get started
Run a client and server, then learn the terms that the other guides use.
- [Getting started](GettingStarted.md) — run the minimal samples, or build a
client and server from NuGet packages.
- [OPC UA concepts](Concepts.md) — applications, endpoints, sessions, the
address space, values, subscriptions, and PubSub.
- [Your first information model](FirstModel.md) — add a model to the Getting
started server, then read, write, and call it from the client.
- [Sample catalogue](Samples.md) — minimal, reference, PubSub, and
companion-model applications.
- [Packages and supported platforms](DeveloperGuide.md#packages-platform-support-and-versioning)
— choose packages and target frameworks.
## 2. Build your application
Choose the path for your application. The paths are independent: for example,
a PubSub application needs neither a client nor a server.
### Client path
Assumes [Getting started](GettingStarted.md).
1. [Dependency injection: client feature](DependencyInjection.md#client-feature)
— configure a client in the .NET Generic Host.
2. [Managed sessions](Sessions.md#3-managedsession--the-connection-state-machine-facade)
— connect, recover from connection loss, and close. To compare the managed
and classic session APIs, see [choosing a session API](Sessions.md#7-putting-it-all-together).
3. [Read, write, and call methods](FirstModel.md#3-use-the-model-from-the-client)
— resolve namespace URIs and browse paths, check the status of each
operation, and call methods through a client generated from the model.
4. [Subscriptions](Subscriptions.md) — callback subscriptions for long-lived
monitoring and streams for short observations.
5. [Generation-bound requests](Sessions.md#generation-bound-client-requests) — retain remote file
handles, history cursors and target classifications without following a
replacement connection.
### Server path
Assumes [Getting started](GettingStarted.md).
1. [Dependency injection: server feature](DependencyInjection.md#server-feature)
— host a server and configure its endpoints, security, and node managers.
2. [Node managers: start with a model](NodeManagers.md#start-with-a-model) —
generate a node manager from your model and attach callbacks.
[Complete method invocation results](NodeManagers.md#complete-method-results-and-diagnostic-forwarding) covers
ordered output values and resolved operation/input diagnostics.
[Your first information model](FirstModel.md) is a complete example.
3. [Runtime NodeSets](RuntimeNodeSets.md#quick-start-examples) — load NodeSet2
models without generated code when models change independently of your
application.
4. [Asynchronous server support](AsyncServerSupport.md) — implement service and
node-manager callbacks asynchronously.
### PubSub path
A PubSub application needs neither a client nor a server, so the Getting
started exercise and the other two paths are optional here.
1. [Concepts: client/server and PubSub](Concepts.md#clientserver-and-pubsub) —
publishers, subscribers, and datasets.
2. [Run a first publisher and subscriber](PubSub.md#run-a-first-publisher-and-subscriber)
— exchange signed and encrypted messages on one computer with the
[reference PubSub sample](../samples/PubSub/ConsoleReferencePubSubClient/README.md).
3. [PubSub guide](PubSub.md) — the fluent builder, hosting, configuration,
encodings, and security.
4. [Transport selection](PubSub.md#transports) — UDP, Ethernet, MQTT, and Kafka.
## 3. Add data types and application services
Assumes the client or server path. Choose the capabilities your application
needs.
### Data types and models
- [Source-generated data types](SourceGeneratedDataTypes.md) — generate
encodeable implementations for your own structures.
- [Complex types](ComplexTypes.md) — decode server-defined structures and
enumerations at run time.
- [Model dependencies](ModelDependencies.md) — compose models that depend on
other models.
- [NodeId assignment](NodeIdAssignment.md) — control the identifiers of nodes
created at run time.
- [Schema generation](SchemaGeneration.md) — produce XSD, BSD, and JSON schemas
for data types.
### Application services
- [State machines](StateMachines.md) — define, drive, and observe state
transitions.
- [Programs](Programs.md) — host and control Part 10 invocations, monitor
captured transition results, and manage diagnostics and lifetime.
- [Alarms and conditions](AlarmsAndConditions.md) — raise, acknowledge, and
stream alarms. Alarm conditions use state machines, for example for shelving.
- [Historical access](HistoricalAccess.md) — store and read value and event
history.
- [Aggregates](Aggregates.md) — calculate processed history; read historical
access first.
- [File system client](FileSystemClient.md) — transfer files through the
standard file objects.
- [Alias names](AliasNames.md) — find nodes through named aliases.
- [Node management](NodeManagement.md) — let clients add and delete nodes and
references.
- [Final-value publication](NodeManagers.md#final-value-publication-before-node-removal) — await terminal Value
notifications in real Publish responses before removing dynamic subtrees.
- [Model change tracking](ModelChangeTracking.md) — keep client caches current
when the address space changes.
- [NodeSet export](NodeSetExport.md) — export a server's address space to
NodeSet2 XML.
## 4. Use companion models
Companion specifications define models for particular industries and device
types; [Concepts](Concepts.md#information-models-and-companion-specifications)
explains how they relate to the base model. These libraries assume the server
path and, for typed client access, the client path. The packages load the
models that each model depends on.
- [Device Integration](DeviceIntegration.md) (OPC 10000-100) —
devices, topology, and locking.
- [Asset Management Basics](AMB.md) (OPC 10000-110) — make devices,
machines, pumps or scales manageable assets:
discovery, identification, health alarms, maintenance, documentation links
and locations. Read Device Integration first.
- [Software update](SoftwareUpdate.md) (OPC 10000-100) —
software package storage, installation, and confirmation. Read Device
Integration first.
- [ISA-95](ISA95.md) (OPC 10030 and OPC 10031-4) — the common
model and job control.
- [Positioning](Positioning.md) (OPC 10000-210 and OPC 10000-211; preview
package) — relative frames and geographic positions.
- [Machinery](Machinery.md) (OPC 40001-1, -2, -3, -4 and -101) —
machines with identification, server-driven state machines,
process values, job management, energy and result transfer, based on the
Industrial Automation, Device Integration, PA-DIM, ECM and ISA-95 models.
- [Pumps](Pumps.md) (OPC 40223) — pumps and vacuum pumps,
published both as Device Integration devices and as Machinery machines.
- [Machine Vision](Vision.md) (OPC 40100-1 and OPC 40100-2) —
released control, recipes, configurations, results, assets, and condition monitoring,
with Vision/Perception composition and Machinery hosting.
- [MachineTool and wireless peripherals](MachineTool.md) (OPC 40501-1 and
OPC 40505) — machine monitoring, tools, production/jobs/files and independently
hosted wireless measurements, configuration and records in one package family.
- [Geometric Measurement Systems](GMS.md) (OPC 40210) — native measurement
equipment, qualification/calibration, production observations and results.
The guide documents the upstream undefined Production-statistics CU exception.
- [Cranes and Hoists](CranesHoists.md) (OPC 40020-1; preview packages) —
Robotics-derived crane systems, equipment observations and explicitly
authorized speed-limit requests.
- [Scales](Scales.md) (OPC 40200 and OPC 30050) — weighing
technology with every scale kind, scale systems, recipes and PackML state
machines, based on the Machinery model.
- [Plastics and rubber capabilities](PlasticsRubber.md) (OPC 40083 and OPC 40082-6) —
shared machine configuration, control and monitoring, with
[production dataset transfer](PlasticsRubber.md#production-dataset-protocol) and
[granulate drying](PlasticsRubber.md#granulate-drying-devices-opc-40082-6).
- [Extrusion](Extrusion.md) (OPC 40084-1 through -12) — the extrusion line
and its device families, optional capabilities, typed clients and composition.
- [Robotics](Robotics.md) (OPC 40010-1; preview package) — motion-device
systems, based on the Industrial Automation and Device Integration models.
The guide's draft Robot Intent model is listed in [stage 7](#7-draft-and-experimental-capabilities).
- [WoT connectivity](WoTConnectivity.md) (OPC 10100-1; preview package) —
connect Web of Things assets. Its registry extension is listed in stage 7.
For more examples, including the Pumps and Machinery models, see the
[companion-model samples](Samples.md#companion-model-samples).
The [generic recycling simulation](../samples/Recycling/README.md) combines a causal production
model with separately hosted process views; its guide identifies the remaining companion
integration limits.
To expose these typed client interfaces to an agent, use the
[industrial companion MCP tools](McpServer.md#industrial-companion-tools). Select one family or
compose several profiles without enabling the entire tool catalog.
The [WoT and xRegistry profiles](McpServer.md#wot-and-registry-tools) cover
asset/registry management and document conversion; the document profile does
not require a UA connection.
## 5. Prepare for production
Builds on the certificate trust you used in [Getting started](GettingStarted.md).
Before you deploy a client or server, work through the
[production readiness checklist](ProductionChecklist.md). It links to these
guides for the details:
1. [Certificates](Certificates.md) — certificate stores, trust, and chain
validation.
2. [Identity providers](IdentityProviders.md) — authenticate users on clients
and servers.
3. [Role-based user management](RoleBasedUserManagement.md) — map identities to
roles and permissions.
4. [Certificate manager](CertificateManager.md) — certificate lifecycle,
rotation, and remote updates.
5. [Diagnostics](Diagnostics.md) — logging, metrics, tracing, auditing, and
packet capture.
6. [Rate limiting](RateLimiting.md) — admission limits and busy signals during
connection storms.
7. [Server resource isolation](ResourceIsolation.md) — per-caller limits and
reserved capacity for startup and recovery.
8. [Profiles and facets](Profiles.md) — implemented profiles and platform
boundaries.
9. [Container reference server](ContainerReferenceServer.md) — run the
reference server in a container.
## 6. Advanced integration, reliability, and scale
Each group names the stages it assumes.
### Transports and integration
Assumes the client or server path.
- [Transports](Transports.md) — UA-TCP, HTTPS, and WebSocket transports.
- [REST binding](WebApi.md) — OpenAPI mapping, encoding negotiation, and HTTP
authentication.
- [OPC UA over OpenAPI](OpenApi.md) — serve the OpenAPI document the stack
generates from its REST routes and call the server from generated REST
clients.
- [Reverse Connect](ReverseConnect.md) — server-initiated connections.
- [Session-less invocation](SessionlessInvocation.md) — let clients call
Read, Browse, Call and the other §6.3 Services without a Session.
- [PubSub external-server adapter](PubSub.md#binding-pubsub-to-an-external-opc-ua-server-client-session-adapters)
— bind PubSub to an OPC UA server through a managed client session. Assumes
the client and PubSub paths.
- [PubSub transcoding](PubSub.md#transcoding) — convert encodings, values, and
metadata between PubSub messages.
- [MCP server](McpServer.md) — let AI agents browse, read, write, and diagnose
OPC UA servers. [Stack workflow profiles](McpServer.md#stack-workflow-tools)
add GDS/credential issuance, roles/users, files, alarms, history, schemas,
policy-controlled PubSub and live WoT execution.
- [WoT / NodeSet conversion](WoTNodeSetConversion.md) and
[WoT protocol bindings](WotBindings.md) — convert Thing Descriptions and add
protocol bindings. Read WoT connectivity first.
### Session recovery and performance
The subscription guides assume the client path; the sizing guides assume
[Diagnostics](Diagnostics.md).
- [TransferSubscriptions](TransferSubscription.md) — move server subscriptions
to a new session.
- [Durable subscriptions](DurableSubscription.md) — keep subscriptions and
queued notifications while clients are disconnected.
- [Generation-bound session clients](SessionBindings.md) — capture dispatch,
session identity and mapping snapshots without reconnecting to a replacement peer.
- [Server scalability](ServerScalability.md) — sizing limits and bottlenecks.
- [Benchmarks](Benchmarks.md) — measured performance and methodology.
### Security infrastructure and fleet management
Assumes [stage 5](#5-prepare-for-production).
- [ECC profiles](EccProfiles.md) — elliptic-curve security policies and their
platform requirements.
- [Crypto providers](CryptoProvider.md) — replace the platform cryptography and
keep private keys in hardware.
- [Provisioning mode](ProvisioningMode.md) — configure a new server securely
before exposing application data.
- [Global Discovery Server](GDS.md) — application registration and central
certificate management.
- [GDS sample](../samples/Gds/README.md) — a runnable onboarding workflow.
- [AuthorizationService](AuthorizationService.md) — issue access tokens.
- [KeyCredentialService](KeyCredentialService.md) — manage credentials for
services that are not OPC UA. Its issued-token bridge is listed in stage 7.
### High availability and deployment
Assumes a working single server and [stage 5](#5-prepare-for-production).
- [High availability](HighAvailability.md) (preview package) — redundancy,
failover, and distributed state.
- [Replica-consistent NodeIds](ReplicaNodeIdentity.md) (preview package) — keep
node identifiers identical across replicas; required before replicating an
address space.
- [Kubernetes](Kubernetes.md) (preview package) — cluster deployment,
discovery, readiness, and secrets. Read high availability first.
- [PubSub high availability](PubSubHighAvailability.md) (preview package) —
redundant publishers and subscribers. Assumes the PubSub path.
### Native AOT publishing
Publish an application as a native executable without a JIT compiler; start
with [Native AOT: publish an application](NativeAoT.md#publish-an-application).
Feature-specific guidance:
- [Servers with generated node managers](NodeManagers.md#nativeaot-publishing)
- [Applications hosted with dependency injection](DependencyInjection.md#native-aot)
- [PubSub applications](PubSub.md#native-aot)
## 7. Draft and experimental capabilities
These guides implement working-group drafts or experimental extensions.
Namespace URIs, NodeIds, and APIs can change before the specifications are
published, so evaluate them before you depend on them in production. Each
guide describes its current limitations.
- [xRegistry](XRegistry.md) (draft model; preview package) — the generic
registry base model, resource storage, and federation.
- [AI model management](AI.md) (draft model; preview package) — model
catalogues, deployments, inference, and learning jobs. Builds on xRegistry.
- [Perception model](Vision.md#perception-model) (draft model; optional OpenUSD renderer is preview-only) — capture, media,
feedback, and client workflows.
- [Robot Intent](Robotics.md#robot-intent) (draft model; preview package) —
task-level motion commands. Does not require the Robotics model.
- [OpenUSD](OpenUsd.md) (draft models; preview package) — bind values to OpenUSD
scenes and materialize scenes in the address space.
- [WoT Connectivity 1.1 registry](WoTConnectivity.md#11-wot-connectivity-11-registry-and-materialization-preview)
(draft model; preview package) — registry and materialization. Read WoT
connectivity first.
- [KeyCredential issued-token bridge](KeyCredentialService.md#experimental-keycredential-issued-token-bridge)
(experimental).
These samples combine several draft or preview capabilities. Read the guides
for their models first:
- [Bin picking cell](../samples/Robotics/BinPickingCell/README.md) — Robot
Intent, Vision, and an OpenUSD scene.
- [Visual inspection cell](../samples/Vision/VisualInspectionCell/README.md) —
Vision, AI model management, and ISA-95 job control.
- [WoT aggregation sample](../samples/WotCon/README.md) — load Device
Integration, Machinery, and Pumps models from WoT documents through the WoT
Connectivity 1.1 registry, and bind them to two OPC UA source servers.
- [Generator sample model](../samples/OpenUsd/GeneratorServer/Generators.md)
(draft model) — generating-set simulation and scene composition.
## Reference and upgrade
- [What's New in 2.0](WhatsNewIn2.0.md) — a summary of new capabilities.
- [Migration Guide](MigrationGuide.md) — upgrade from 1.5.378, with
[topic-specific 2.0 guides](migrate/2.0.x/README.md) and
[PubSub migration](migrate/2.0.x/pubsub.md).
- [Reference client](../samples/Reference/ConsoleReferenceClient/README.md) —
command-line configuration and transport profiles.
- [Reference server](../samples/README.md) — hosting and compliance-test setup.
- [Reference PubSub client](../samples/PubSub/ConsoleReferencePubSubClient/README.md)
— publisher, subscriber, and external-adapter modes.
The Windows Forms reference applications are maintained in the
[Samples repository](https://github.com/OPCFoundation/UA-.NETStandard-Samples).
## Contributing and maintaining the SDK
These documents describe building and maintaining this repository, not using
the SDK in an application:
- [Developer Guide](DeveloperGuide.md) — prerequisites, build, tests, and coding
conventions.
- [Continuous integration](DeveloperGuide.md#continuous-integration) —
pipelines and coverage gates.
- [Native AOT test harness](NativeAoT.md#test-harness-overview) — build, run,
and extend the Native AOT compatibility tests.
- [Release process](ReleaseProcess.md) — release branches, versioning,
backports, and recovery.
- [Redundancy sample tests](RedundancySampleTests.md) — process-level failover
and soak validation.
- [Fuzz testing](../fuzzing/Fuzzing.md) — encoder, certificate, and network
campaigns.