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Extensibility Architecture

Philosophylink

Font design workflows vary considerably across designers. The Counterpunch Font Editor provides a foundation that can be customized and extended to match your process.

Rather than providing hundreds of built-in features, the editor offers several pathways for adding the functionality you need. Whether you script in Python, build JavaScript extensions, or integrate the editor into a larger toolchain, the architecture provides multiple integration points.

The Font Modellink

At the heart of the editor is a babelfont-ts object model—a JavaScript-based representation of the complete font data structure accessible to all layers of the system. This shared model means that changes made through the UI, Python scripts, or JavaScript extensions all operate on the same data, with modifications immediately visible across the entire application.

JavaScript: Runtime Extensibilitylink

Load JavaScript code dynamically at runtime to extend the editor without touching the core codebase. Your code has direct access to the babelfont-ts font model—the same object structure that powers the UI. Read font metadata, modify glyph outlines, adjust spacing, manipulate OpenType features, or transform design space coordinates. Changes are immediately visible in the interface.

Integration Approaches

JavaScript extensions can work at multiple levels:

Direct data access: Manipulate the font model programmatically, implementing transformations and tools that go beyond the built-in UI.

Event subscription: React to user actions, selection changes, and document modifications in real-time. Build workflows that respond to what’s happening in the editor.

UI extension: Add custom interface elements, panels, and visualizations. The browser’s DOM is fully accessible.

Note on UI stability: While direct DOM manipulation is possible, use the plugin infrastructure when available. The editor’s internal DOM structure may change between releases. The plugin API provides stable integration points maintained across versions.

Python: Scripting Powerlink

Through Pyodide, a Python environment runs in your browser with access to the babelfont-ts font model—the actual live object that powers the editor.

Python code can read and modify font data directly. Changes appear immediately in the UI without an import/export cycle. Python sees the same object structure as JavaScript.

Many Python packages are available—fontTools, numpy, and other pure Python libraries. Packages can be loaded at runtime as needed. Python functions can subscribe to editor events, enabling reactive scripts. You can build automation tools, batch processors, or analysis scripts that operate on live data.

Note that Pyodide runs in a WebAssembly environment, which means only pure Python packages and packages with compiled WebAssembly builds will work. Packages requiring native C extensions not compiled for WebAssembly won’t load.

WebAssembly: Performance Where It Matterslink

The editor’s font compilation engine is written in Rust and compiled to WebAssembly, delivering native-speed performance for computationally intensive operations in the browser.

You can build custom WASM modules for specialized font processing and load them dynamically at runtime. These modules interact through JavaScript as an intermediary—there’s no direct WASM-to-WASM communication. This keeps the integration surface clean and allows independent development of modules.

The architecture prioritizes flexibility over raw speed at the boundary: crossing between JavaScript and WASM requires data serialization. For modules that communicate frequently, this overhead can be measurable. But for focused, computationally intensive tasks, WASM delivers the performance gains where they matter most.

Yjs: Real-Time Data Streaming (Planned)link

A planned Yjs integration will emit granular edit operations as they occur. External tools can subscribe to this stream of changes for quality assurance, collaborative workflows, or analysis—all without coupling to the editor’s internals. Think of it as a data feed that external applications can consume and react to in real-time.

Cross-Tab Communication: Build Your Toolchainlink

The editor publishes structured events through the browser’s window.postMessage API, enabling communication between tabs and windows. This creates possibilities for specialized tool ecosystems without tight coupling.

After compiling a font, the editor can emit binary font data that quality assurance tools in other tabs can ingest for validation, visualization, or testing—all client-side, no server required. Tools run in isolated security contexts, subscribing only to the message types they need.

Unlike direct JavaScript event access, postMessage provides a curated interface with well-documented message formats. The editor controls what gets published; external tools consume what’s relevant to them.

Design Principleslink

Meet users where they are: Script in Python if that’s your language. Build extensions in JavaScript if you’re a web developer. Use WASM for performance-critical processing. Each pathway serves different needs and skill sets.

Open, not overwhelming: Rather than shipping hundreds of features, the editor provides the foundation for building what you need. Extensibility allows the tool to adapt to different workflows.

Standard technology: The editor uses standard browser APIs and widely-used frameworks. A plugin API provides stable integration points for UI extensions, while direct access to browser APIs and the font model remains available for lower-level work.

Shared data, multiple interfaces: The babelfont-ts model is the single source of truth accessible from every layer. Whether you’re scripting in Python, extending with JavaScript, or building UI with the DOM, you’re working with the same live data.

This architecture creates a font editing environment that adapts to workflows we haven’t imagined yet—because you can build the parts we didn’t.