Syside
Syside is a SysML v2 tool suite for model-based systems engineering. Models are written as plain text, versioned in Git, validated in real time, and turned into diagrams, tables and reports through a Python API.
What is Syside?
Syside is a SysML v2 tool suite for model-based systems engineering, built by Sensmetry UAB, a Lithuanian company based in Vilnius with a Swedish branch in Uppsala and a US subsidiary in Delaware. Its governing idea is what the vendor calls System-as-Code: the system model is written and stored as plain text, so it can live in Git beside the software it describes.
The suite has three commercial parts. Syside Editor is a free Visual Studio Code extension providing syntax and semantic highlighting, autocompletion, auto-formatting, a document outline, hover documentation and cross-workspace navigation. Syside Modeler adds visualisation: diagrams generated directly from the text, editable table and matrix views that write changes back into the source, a views explorer listing every view definition in the project, and a headless command line interface. Syside Automator is a Python library that opens the model to code, letting you create, update, delete and move elements, evaluate expressions, constraints and SI quantities, check that assumptions imply requirements, and generate reports with any Python reporting library. A separate open-source package manager, Sysand, handles model library dependencies.
Validation is what the vendor emphasises most. Syside checks SysML v2 syntax and semantics in real time, and every diagnostic points back to the specification rule it enforces. Diagrams export to PNG, SVG and PDF, tables and matrices export to CSV, and all of it can run headlessly inside a pipeline. Requirements travel both ways through ReqIF, connecting the model to Codebeamer, IBM DOORS and Polarion.
The AI angle is deliberate rather than incidental. Sensmetry positions the textual model as something an AI assistant can read and contribute to, and Syside Cloud, a browser-hosted environment aimed at courses and workshops, ships with Modeler, Automator and Claude preloaded.
The tools run on Windows, macOS and Linux and require Visual Studio Code, VS Codium or Cursor, plus Python 3.12 or newer and a Java 21 runtime. Sensmetry claims more than 20,000 users and cites engineers in automotive, aerospace and defence, with named references at DLR, OHB System AG and JPL. The vendor is an active contributor to the OMG SysML v2 specification. Version numbering remains below 1.0.
What it does
- Write and validate SysML v2 models in textual notation inside Visual Studio Code, with errors flagged against the specification rule they break
- Generate diagrams automatically from the text, then click any element to jump straight back to its definition
- Inspect and edit the model through spreadsheet-style table and matrix views whose cells write changes back into the source
- Query, edit and evaluate models programmatically through the Automator Python API
- Run validation, formatting and diagram export headlessly in CI/CD pipelines using the command line interface
- Move requirements both ways through ReqIF to Codebeamer, IBM DOORS and Polarion
- Version models in Git with the same branches, pull requests, diffs and merge conflict resolution used for code
When to use Syside / When not to
A quick filter to help you decide if Syside is the right fit.
When to use Syside
- Systems engineers adopting SysML v2 who want to write models in textual notation rather than draw them
- Engineering teams that already live in Git and want models to follow the same branching, review and merge workflow as their code
- Automotive, aerospace, space and defence teams building complex cyber-physical systems, including those needing air-gapped deployment
- Automation-minded engineers who want validation, diagram export and traceability reports running headlessly in CI/CD pipelines
- Lecturers, trainers and consultants teaching SysML v2, who get a free academic licence and a browser-based classroom environment
When not to use Syside
- Practitioners committed to diagram-first SysML v1 modelling, for whom the shift to a text-first workflow is the main friction the vendor itself reports
- Buyers who need a published price before engaging: no figure appears on the pricing page and the Business plan is quote-only
- Anyone wanting to model on a phone or tablet, since the tools are desktop-only on Windows, macOS and Linux
- Teams unwilling to depend on Visual Studio Code plus separate Python and Java runtimes on every workstation
- Engineers who need to simulate and execute models today, as that capability is still advertised as coming soon on both paid plans
How to use Syside
A typical end-to-end flow, from setup to results.
- Check the prerequisites: Windows 10 or later, macOS 14 or later, or Linux, plus Visual Studio Code 1.91 or newer (VS Codium and Cursor also work), Python 3.12 or newer and a Java 21 runtime
- Install the free Syside Editor extension from the Visual Studio Code Marketplace or Open VSX and start writing .sysml files, with no account required
- Use real-time validation, autocompletion and navigation to learn the notation, following each diagnostic back to the specification rule it cites
- Start the 30-day Solo trial to unlock Modeler and Automator; payment details are collected up front through Paddle and the subscription begins automatically unless cancelled
- Generate diagrams from any element or view, and open table and matrix views to inspect and edit the model like a spreadsheet
- Commit a syside.toml file to the repository so formatting stays consistent across every contributor
- Import existing requirements through ReqIF from Codebeamer, IBM DOORS or Polarion, and export the updated model back
- Script the model with the Automator Python API, following the reference documentation, and wire validation and diagram export into your CI/CD pipeline through the headless CLI
- For teams, contact sales for the Business plan to obtain CI/CD entitlement, floating or perpetual licences, cloud deployment or an air-gapped installation
- For teaching, request the free academic licence with proof of status, or ask for a Syside Cloud environment provisioned for your training dates
Pros & Cons
Pros
- Plain-text models mean every existing Git workflow applies unchanged, with branches, pull requests, diffs, blame and merge conflict resolution
- Validation is anchored in the SysML v2 specification, and each diagnostic names the rule it enforces rather than merely reporting an error
- A genuinely permanent free tier, Syside Editor, sits alongside a 30-day trial on the paid Solo plan and a free renewable academic licence
- An unusually explicit non-collection commitment: neither the models, nor telemetry, nor in-application usage are collected, and the licence puts model ownership with the customer
- A publicly documented Python API and headless CLI make the tool automatable rather than merely interactive
- Air-gapped deployment is offered for classified and network-isolated environments, alongside Windows, macOS and Linux support
- The vendor contributes to the OMG SysML v2 specification and cites verifiable references at DLR, OHB System AG and JPL
Cons
- No price is displayed anywhere: the pricing page carries no figure in its HTML and fetches the Solo amount at display time through Paddle, so what you see depends on your location
- The Business plan, which alone unlocks CI/CD entitlement, cloud and air-gapped deployment and offline installation, is quote-only
- Three separate prerequisites must be installed before starting: Visual Studio Code or an equivalent, Python 3.12 or newer, and a Java 21 runtime
- Model execution and simulation are still marked as coming soon on both paid plans
- Version numbering remains below 1.0, with 0.10.3 current and 0.11.0-rc.1 in preview
- Transparency gaps on the legal side: no data processing agreement is published or mentioned, no named subprocessor list exists, and no minimum age is stated
- The privacy policy contradicts itself on usage data between sections 1.4 and 1.5, and declares itself governed by the laws of England and Wales despite a Lithuanian controller
Pricing & Plans
A permanent free plan exists: Syside Editor is available at no charge from the Visual Studio Code Marketplace and Open VSX. The lowest paid entry point is the Solo plan, billed per user per month either monthly or annually, with the annual commitment advertised at 37% off and preceded by a 30-day free trial. No amount can be quoted here, and none should be inferred: the pricing page contains no figure in its markup and retrieves the Solo price at display time through Paddle, which returns an amount and a currency determined by the visitor's location. The Business plan is quoted on request. A free academic licence is available to students and teachers, and Syside Cloud is priced per training cohort.
- permanently free
- includes Syside Editor only
- providing basic textual SysML v2 editing support in Visual Studio Code
- paid subscription per user per month
- billed monthly or annually with the annual option advertised at 37% off
- includes Syside Modeler and Automator
- a 30-day free trial and priority support
- for one authorised user per licence
- quoted on request
- everything in Solo plus CI/CD integration
- custom application development support
- cloud development environment support
- perpetual and floating licensing options
- air-gapped deployment and enterprise support
- for an agreed number of users
- free non-commercial licence for students and teachers
- granted on proof of status
- one-year default duration and renewable at the vendor's discretion
- browser-hosted environment priced per training cohort according to participant count and duration
- with a significant discount for academic use
Data, GDPR & hosting
A consolidated view of how Syside handles your data.
GDPR overview
GDPR compliance is stated explicitly. The privacy policy, last updated 11 June 2026, names UAB Sensmetry as lead data controller for the purposes of the GDPR and UK GDPR, and covers the Lithuanian company, its Swedish branch and its US subsidiary. It sets out the legal bases relied on (consent, contract, legal obligation, legitimate interests, vital interests) and the full set of data subject rights: access, rectification, erasure, restriction, portability, objection, no automated decision-making, and withdrawal of consent, all exercised through legal@sensmetry.com. Complaints may be brought to a member state authority, the UK ICO or the Swiss commissioner. Processing is described as primarily within the EEA, with Standard Contractual Clauses and encryption covering transfers beyond it. No DPO and no Article 27 representative are designated, which is consistent with a controller established inside the Union. One oddity: the policy declares itself governed by the laws of England and Wales.
Who owns the data?
Clause 5.2 of the licence agreement is unambiguous: you keep all right, title and interest in the models you create with Syside, including the intellectual property in them. Sensmetry retains ownership of the software and documentation, which are licensed to you rather than sold. The vendor goes further than most on the model side. Its privacy policy states that it collects no information about the models built with any component of the suite, and clause 14.3 of the licence commits it to collecting no usage data or analytics about how the software is used. Payment details are held by Paddle, the merchant of record, and not by Sensmetry.
Reuse rights
Because the models are yours, you may reuse, publish, export and commercialise them without asking Sensmetry for permission; the licence gives the vendor no rights over your model content. What is restricted is the software itself: you may not rename the licensed applications or ship them inside releases with materially different functionality without prior written approval, and academic licences forbid commercial use altogether. On the vendor's side the data footprint is narrow, covering identity and contact details, an IP address when the software validates its licence, and the licence key and activation status; website logs, cookies and Google Analytics apply to the marketing site. One inconsistency deserves flagging: section 1.4 of the privacy policy states that no telemetry and no in-application usage tracking are collected, while section 1.5 lists data on your use of and interaction with the licensed software among the information that may be processed.
Data retention & training
Hosting summary
Sensmetry describes processing as taking place primarily within the European Economic Area, and the wording is deliberately not absolute. The company states that it uses service providers in several geographical locations, and that it and those providers may transfer personal data to, or access it from, jurisdictions outside the EEA. For the hosted service, customers can choose where the service runs, and if they choose a location outside the EEA, personal data is transferred there. Transfers outside the EEA are covered by Standard Contractual Clauses or other appropriate safeguards, with additional protections such as encryption applied by the providers. No hosting country is named and no cloud provider is identified: the policy lists only categories of third parties, namely cloud computing services, data analytics services, data storage providers and payment processors, with Paddle named as the payment processor and Google Analytics as the analytics service on the website. Note that the marketing site itself resolves to a server in Germany, which says nothing about where customer data is held.
Things to keep in mind
Risks and trade-offs to weigh before adopting Syside.
- You cannot budget for this tool from the website: no price appears in the page itself, the figure is fetched from the payment provider at display time and varies with your location, so check it yourself and get the Business quote in writing
- The Solo trial requires payment details up front and converts into a paid subscription automatically after thirty days unless cancelled, and payments are non-refundable outside the cases listed in the licence
- Real-time validation is reassuring but can breed complacency: a model that passes every specification check can still describe the wrong system, and no tool substitutes for engineering review
- Letting an AI assistant read and contribute to safety-relevant models invites unexamined acceptance of generated content; treat AI output as a draft requiring the same scrutiny as any other contribution
- The privacy policy contradicts itself on usage data between sections 1.4 and 1.5, and declares itself governed by the laws of England and Wales although the controller is Lithuanian, so verify the position before relying on it contractually
- No data processing agreement is published or mentioned, no named subprocessor list exists, and hosting is described only as primarily within the EEA with the customer free to choose another location, which matters if you handle regulated or export-controlled content
- Capability planning risk: model execution and simulation are advertised as coming soon on both paid plans, and version numbering is still below 1.0, so do not build a roadmap on features that are not yet shipped
Setup & Integrations
Technical difficulty
Moderate, and aimed squarely at people already comfortable with a code editor. The free Editor installs in one click from the Visual Studio Code Marketplace with no account. Modeler and Automator additionally require Python 3.12 or newer and a Java 21 runtime on each workstation, and formatting is configured through a syside.toml file committed to the repository. Air-gapped installation is a deliberate multi-step process involving offline downloads, licence file generation and physical transfer. Syside Cloud exists precisely to remove setup entirely, giving browser access with a Google or email sign-in.
Deployment
Integrations
Behind Syside
Social
Resources
All the official URLs gathered for verification and reference.
Frequently asked questions
Is there a genuinely free version of Syside?
How much does the paid plan cost?
What do I need installed before I can use it?
Are my models sent to Sensmetry?
Who owns the models I create?
Does Syside offer an API?
Can it connect to my requirements management tool?
Can Syside run offline or in an air-gapped environment?
Is there anything for students and teachers?
How do I cancel a subscription?
Should you pick Syside?
Syside is a focused tool, not a general-purpose assistant, and it is better for it. Its bet is that a system model should be plain text: written in an editor, reviewed in a pull request, validated by a pipeline, and read by an AI assistant as easily as by a colleague. For teams that already work this way with software, the fit is immediate, and the Git story alone removes a category of tooling that graphical SysML environments still require.
The engineering substance holds up. Validation is tied to the specification rather than to a vendor's interpretation, diagrams and tables are live views of the model rather than copies, and the Python API plus headless CLI make the whole thing automatable. The free Editor is a real permanent tier, the academic licence is generous, and the commitment to collect neither models nor telemetry is unusually specific for a business tool, with model ownership written into the licence rather than merely promised on a page.
The reservations are mostly about transparency and maturity. No price is visible anywhere on the site because the figure is fetched from the payment provider when the page loads, which makes the Solo plan impossible to budget without visiting in person, and the Business plan is quote-only. Model execution is still promised rather than delivered. Version numbers remain below 1.0. On the legal side there is no published data processing agreement, no named subprocessor list, no stated minimum age, and a privacy policy that contradicts itself on usage data and picks an odd governing law for a Lithuanian controller.
Worth a serious look if you are moving to SysML v2 and want your models to behave like code. Try the free Editor first, then measure whether the textual shift suits your team before committing.
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