Jess

Jess is in very early alpha. The public entry point is still narrow and moving, with rough edges and missing pieces while the language surface settles.

Jess is a stylesheet language and a compiler, designed for teams that want modern CSS ergonomics without giving up compile-time power. The public alpha ships today through Less-compatible tooling, but the project itself is broader: Jess is the language direction, with richer composition, expressions, and module boundaries that still compile down to CSS.

The project starts by earning trust on familiar Less workflows, then opens out toward broader Jess syntax and composition over time.

Why a preprocessor at all?

CSS keeps gaining power — custom properties, nesting, color-mix(), container queries — but a build-time layer still earns its keep:

• Reuse without runtime cost. Variables, mixins, and functions resolve at compile time and ship as plain, static CSS.
• Organization that scales. Split styles across files and compose them back together with real module boundaries.
• One source of truth for tokens. Define colors, spacing, and typography once and derive the rest.

Jess is being designed around expressions, live bindings, collections, and a JS/TS/JSON module system while still producing CSS output by default.

Where to next

• Set up: Installation and Configuration.
• Learn the module system: Modules & imports.
• Migrating an existing codebase: Migrating to Jess, or Coming from Sass.
• Editor experience: VSCode & Cursor support.