Windows
x64 installer
The Windows installer is on its way.
The OPC UA client that shows what the session negotiated.
Browse, read, write, subscribe and call methods on any OPC UA server. See what was requested and what the server revised, review every certificate before you trust it, and read each service call as decoded UA Binary. Native Rust, with no browser engine inside.
From the value that looks wrong to the call that explains it.
A dense, keyboard-first workspace where values, negotiated parameters and service calls get the room and the chrome steps back. Every screen here is the real app, shown on its built-in simulator's fictional water-treatment plant.
A grid of monitored items with value, unit, StatusCode and timestamps. A Bad value is struck through, an Uncertain one is in italics and a stale one shows its age, so none of them passes for a plain number. When the device's clock runs behind the server, the inspector says so.
Requested next to revised, always: publishing interval, keep-alive, lifetime, sampling and queue size. A timeline of data changes, keep-alives and PublishRequests, and when an item overflows its queue a notice with a one-click fix that sends ModifyMonitoredItems.
The service calls of the session (up to the last 5,000) as rows, request paired with response, with latency and status. Select one and it is decoded field by field, with the bytes of each field. On an encrypted channel it shows the message as the client encoded it, and says what the size was on the wire.
A write shows the Variant bytes and the WriteValue before anything is sent. On a live plant it asks you to type the node's name, and afterwards it reads the value back and compares it, so a clamped value is not a surprise. Read-only connections hide every write.
Inputs are typed from the method's InputArguments and validated before the call. The request's bytes are previewed, and the result shows each output and the status of each input argument. On a live plant the call asks for the method's name first.
Every attribute of a node in one Read, its references in both directions, and the same NodeId in three notations: the session's ns= index, the portable nsu= URI and the browse path. A switch in the status bar changes every grid at once.
HistoryRead raw, or processed with an aggregate, over a range you choose. Continuation points are paged and released, a gap in the data is drawn as a gap, never as an interpolated line, and the status bits of each value stay visible. Export CSV.
Retained conditions with severity, active, acknowledged and confirmed state, filled by ConditionRefresh, and an event log that shows the EventFilter it sent, clause by clause, with what the server said about each. Acknowledge and Confirm with a comment use the condition's latest EventId, and say so when it went stale.
Paste the hex of one or more UA TCP chunks (MSG, HEL, ACK, ERR, OPN, CLO) from a capture or a log (unencrypted ones; the Trace's copies already are) and read them field by field, with the message size checked against the bytes. Or open a message from the Trace in it.
A subscription is a YAML file you can keep in git, with NodeIds stored by namespace URI and never by index. Opened on a server, it reports which nodes resolve and which do not, and subscribes only the ones that do.
A built-in OPC UA server with a water-treatment plant to browse, subscribe to, write and call, over None and Basic256Sha256. Fault switches test a client against a bad sensor, frozen timestamps, lost PublishResponses, a short token lifetime or an expired certificate.
Every server, by site.
A SCADA server in the plant, a historian, a PLC on the bench and the built-in simulator sit in one explorer, grouped by site, each with its own color and with what you are allowed to do to it.
- opc.tcp, with the security you choose
- Security policies None, Basic256Sha256, Aes128_Sha256_RsaOaep and Aes256_Sha256_RsaPss, in the modes None, Sign and SignAndEncrypt. Basic128Rsa15 and Basic256 are tagged deprecated, and neither they nor None are ever preselected: the app ranks the endpoints itself instead of trusting the server's securityLevel.
- Anonymous, user name or user certificate
- Each is offered only if the endpoint you picked offers it. The password goes to your system's credential store when you save (an encrypted file where there is none), never into the server list, and the app refuses to send one that would travel in clear. A user certificate's private key can have a passphrase (RSA, AES-encrypted), kept the same way.
- Grouped by site, colored by server
- Mark a server as a live plant and its color tints the toolbar, the tab and the status bar, so it never looks like the bench, and writes, calls and acknowledgements ask first. A read-only server hides them entirely.
- The address you typed
- Some servers announce a host name that does not resolve from your network. OPC Studio warns, and by default keeps the host you typed, with the port and path the endpoint announces.
- Test it before it is saved
- Test connection runs the whole connect without saving anything and says in plain words why it failed. Servers move between machines as one JSON file, without passwords; an imported server with a user name asks for its password the first time.
Servers
- TSTreatment SCADAscada01.wtp.example:4840Live plant
- PHPlant historianhist01.wtp.example:62541Read-only
- LPLab PLC192.168.10.20:4840Bench
- SMBench simulatorlocalhost:4841Built-in
- L2Line 2 edge gateway10.4.2.15:4840Untrusted
- PZPalletizerCertificate rejectedRejected
Live plants ask before any write Read-only hides them
Certificates without fear.
Clients that accept everything teach you to ignore certificates, and clients that just fail leave you lost. OPC Studio stops before the secure channel opens, shows you the server's certificate with real checks, and answers plainly when a server turns you down.
First contact
An unknown certificate opens a review with its thumbprint in large type, to compare with the one the device shows itself. Nothing more is sent to the server until you decide.
- Valid nowWithin its validity, with five minutes of clock difference tolerated; a warning 30 days before it expires.Warn
- Host matchesThe host name or address you connect to is in the certificate's alternative names.Warn
- ApplicationUri matchesThe server's ApplicationUri is one of the certificate's URI names.Warn
- UsageKeyUsage and ExtendedKeyUsage fit an OPC UA application.Warn
- Key fits the policyA key of 2048 to 4096 bits, and a signature the policy allows: SHA-1 fails the Sha256 policies.Fail
- IssuerSelf-signed with a signature that verifies, or issued by a CA in your issuers folder. Anything else says the trust applies to this certificate only; a broken signature fails.Pass, Warn or Fail
Each check ends as Pass, Warn or Fail. While one fails, both trust buttons are disabled and the dialog says why. Otherwise you can reject the certificate, trust it for this session, or trust it permanently.
When it goes wrong
- The server does not trust you yet
- When a server drops the connection or answers Bad_SecurityChecksFailed, OPC Studio says the server most likely does not trust this client, and gives you its own thumbprint to find in the server's trust list.
- Login refused
- A rejected user name, password or signature says so, and offers Fix credentials, instead of a bare status code.
- Our own certificate
- An invalid URI, an invalid time or a refused use of the client certificate is reported as being about your side of the handshake.
- A changed certificate
- If the certificate you reviewed changes during the connect, or differs from the one you trusted on a given date, the connection stops and says so in red.
- A clear password
- A password that would travel unencrypted is refused before it is sent, with the reason.
A trust list you can read
Certificates live in your data folder in the usual pki/ layout, named after their common name and SHA-1 thumbprint, so you can manage them by hand. A rejected certificate wins over a trusted one. Your own certificate is created on first start, and you can export its public half from the Certificates panel. Revocation lists are not read yet.
pki/
├─ own/
│ ├─ cert.der
│ └─ private/key.pem
├─ trusted/
│ ├─ certs/
│ └─ crl/
├─ rejected/
│ └─ certs/
└─ issuers/
├─ certs/
└─ crl/
Light or dark, it is the same tool.
Twin dark and light themes, dark by default, built to sit next to your IDE. Drag to compare.
And the rest of the toolbox
- Problems first
- Untrusted certificates, refused sessions, Bad or stale items and clock differences are listed most severe first and counted in the status bar, and each opens the tab that shows it. Unacknowledged alarms have their own count on the bell.
- Live chart
- Plot up to four numeric items of a subscription as they are published, with now, min, average and max for each, and a notice when the series mix units.
- Server page
- State, uptime, ServiceLevel, the server's clock against this computer's, round trip, the session and the secure channel, BuildInfo, OperationLimits and the NamespaceArray.
- Recording
- Record a session's values to CSV and its traced messages to a trace file, then reopen the recording read-only in the Trace and Chart views.
- NodeId notations
- ns= index, nsu= URI or browse path, for every grid and inspector at once. Files store only the URI form, because an index belongs to one server session.
- Command palette
- Ctrl K (Cmd K on macOS) reaches every server, subscription, node, method and action without hunting through the tree.
- Import and export
- Move servers between machines as one JSON file with their sites, never with passwords. Importing never overwrites a server silently: it asks whether to rename or replace.
- Event log
- The last 2,000 events the server sent, with the EventFilter that selected them in plain view and the start and end of each refresh marked.
- Fonts and icons inside
- Inter, JetBrains Mono and the Lucide icons are embedded in the app, so it looks the same on every system with nothing else to install.
Nothing leaves your machine.
Read the privacy policy- No account
- Install it and connect. There is nothing to sign into.
- No telemetry
- No analytics and no update checks. The app talks only to the OPC UA servers you set up and to its own simulator.
- Your files
- Servers, certificates and the trust list stay on your computer; recordings go to a folder in your data folder, and watch lists, CSV exports and exported server lists are saved where you choose.
- Native and MIT licensed
- Rust with egui, from one codebase for macOS, Windows and Linux, with no runtime to install, under the MIT license.
Download OPC Studio
Version 0.1.0, free and open source.
Your system
macOS
Apple silicon
A disk image for Macs with Apple silicon.
Linux
x86_64
The .deb package and the AppImage are on their way.
Builds are not code-signed yet: a downloaded copy on a Mac may be reported as damaged until you clear its quarantine flag (xattr -dr com.apple.quarantine "/Applications/OPC Studio.app" in Terminal), and Windows shows a SmartScreen warning.