We are delighted to announce the launch of the Concerto Playground, a live, browser-based environment for authoring, exploring, and sharing Concerto data models.
No installation. No sign-in. Just open the URL, sketch a domain model, and watch it compile to twelve target languages.
What is Concerto?
Concerto is the Accord Project’s open-source data modeling language. It gives you just enough structure to capture real-world business concepts while staying readable by engineers and domain experts alike.
Where JSON Schema or XSD tend to become implementation artifacts owned by developers, a Concerto model is designed to be a shared source of truth: precise enough to drive validation and code generation, human enough to be reviewed and understood by product, legal, operations teams (and agents!).
What the Playground offers
Graph view
The most distinctive feature of the new playground is its interactive class diagram. Select Graph view and your Concerto model renders as a live graph: concepts become nodes, relationships become typed edges, inheritance shows as directed links. You can pan, zoom, and explore the full structure of a complex model without losing your place in the .cto text.
This view was designed and implemented by Sonia Duma, from the University Politehnica of Bucharest, Faculty of Automation and Computer Science. Sonia’s contribution brought a visual way to understand a data model that works for engineers and non-engineers alike. The graph updates live as you type, so the diagram is always a faithful reflection of the current schema, not a snapshot from a generation step.
Code view
Switch to Code view and the right panel shows the generated output for your selected target language, regenerating within a few milliseconds of every keystroke. Tabs across the top switch between TypeScript, Java, Go, C#, Rust, JSON Schema, GraphQL, Protobuf, Avro, OpenAPI, OData, and XML Schema.
The full Concerto toolchain runs client-side. There are no server round-trips; your schema never leaves your browser.
Shareable URLs
Click Share URL and the playground encodes your entire model into the URL. Paste the link and anyone opens the playground with your schema pre-loaded without an account, server storage, or expiry.
Get started
Try the playground: concerto-playground.accordproject.org
Three examples are pre-loaded to give you something to explore immediately. Switch view modes, change a field type, and watch the graph, the generated code, and the form editor all update together.
Contribute: The playground is open-source at github.com/accordproject/concerto-playground under the Apache-2.0 license. Issues and pull requests are all welcome. The codebase is a Vite + React + TypeScript app and the contribution bar is intentionally low.
Join the community: Come and talk to us on Discord. The Technology Working Group meets weekly and we would love to hear how you are using Concerto.
Thank you
The Concerto Playground would not exist without the contributions of the open-source community. Special thanks to Sonia Duma for the graph editor that makes the playground worth showing to anyone, and to Rishabh Jain for squashing some bugs before launch. The Concerto core libraries that power the playground (concerto-core, concerto-codegen, and concerto-cto) are the product of years of work by the Accord Project community.
If you build something with Concerto, we would genuinely like to know. Post in Discord, open an issue, or drop a line to the working group. The playground is live, go try it!
Accord Project is an open-source initiative under the Linux Foundation. All software is released under the Apache-2.0 license. Concerto source code lives at github.com/accordproject/concerto.