marionettejs/marionette

Marionette is a JavaScript library built for agent-led development that provides structure for building interfaces with Backbone applications.

The tool addresses the challenge of giving coding agents a consistent, predictable way to build user interfaces by establishing clear ownership boundaries for different concerns. Views handle rendering content and local interactions, Regions manage View replacement and destruction, and Applications coordinate feature readiness and lifetime. This separation gives agents repeatable patterns for composing features without requiring them to invent architectural decisions from scratch. The library includes version-matched contracts, TypeScript declarations, an ESLint rule against private framework access, and stable diagnostic codes to help agents catch mistakes in generated code.

Marionette v5 is designed specifically for agent-led development workflows and differs from earlier versions by supporting native DOM without requiring Backbone or jQuery, though existing Backbone applications can integrate their Models and Collections through optional adapters. The tool ships with documentation and an agent skill, and provides documentation MCP access that connects API references to supported agent clients. Developers upgrading from v4 should consult the migration guide. The library emphasizes runnable examples and public behavior checks to verify interaction, cancellation, replacement, and cleanup patterns.

The project maintains v4 with maintenance fixes while v5 development continues as a release candidate. The codebase includes automated CI workflows and publishes to npm. Documentation covers agent entrypoints, consumer tooling for skill and plugin installation, lint configuration, type support, and installed documentation lookup.