Kelvin

A declarative language for building web applications. An on-going experiment in building a new programming language with Claude Code.

Define your data models, APIs, admin interfaces, and access control in a single file. No boilerplate, no code generation, no framework to learn.

app Blog {
  entity Post {
    title: text(1..200)
    body: text(1..50000)
    published: bool = false
  }

  view public {
    visibility: public

    list Post {
      show: title, created
      where: published
      order by: created desc
    }
  }

  view admin {
    list Post {
      show: title, published, created
      actions: edit, delete
    }
  }
}

$ kelvin serve blog.kelvin
Server running at http://localhost:3000

That's it. You have a database, REST API, and admin panel.

Features

• Declarative syntax - Describe what you want, not how to build it
• Instant API - REST endpoints generated automatically from your schema
• Built-in admin - A working admin interface out of the box
• Authentication - JWT-based auth with user registration and login
• Hot reload - Edit your .kelvin file and see changes instantly
• Type validation - Rich type system with constraints (text(1..100), email, int(0..*))
• SQLite storage - Zero-config database that just works

Quick Start

Install

npm install -g kelvin-lang

Create your first app

Create a file called app.kelvin:

app HelloWorld {
  entity Message {
    content: text(1..500)
  }

  view messages {
    visibility: public

    list Message {
      show: content, created
      order by: created desc
    }

    create Message {
      input: content
    }
  }
}

Run it

kelvin serve app.kelvin

Your API is now running:

# Create a message
curl -X POST http://localhost:3000/api/messages/message \
  -H "Content-Type: application/json" \
  -d '{"content": "Hello, World!"}'

# List all messages
curl http://localhost:3000/api/messages/message

Documentation

• Language Specification - Complete reference for the Kelvin language
• Tutorial - Build a guestbook in 5 minutes
• Examples - Sample applications

Project Status

Kelvin is in active development. The core features work:

• Entity definitions with validation
• Public and authenticated views
• List, create, edit, delete operations
• User authentication (JWT)
• Admin interface
• Hot reload

See kelvin-spec.md for the full roadmap.

VS Code Extension

Syntax highlighting for .kelvin files is available in the vscode-kelvin directory.

To install:

1. Open VS Code
2. Run code --install-extension vscode-kelvin/kelvin-lang-0.0.1.vsix

Or copy the vscode-kelvin folder to your VS Code extensions directory.

Contributing

Contributions are welcome! Please read the language spec before contributing to understand the design philosophy.

License

MIT