OpenType Tools.

Drop a font file in the browser to see what's inside: glyphs, features, language support, metadata, and table data. OTF, TTF, WOFF, and WOFF2 supported. Includes a text viewer and waterfall. Nothing goes to a server.

A macOS font viewer focused on text shaping and feature behavior. Load multiple fonts, run the same text through all of them, and toggle features on and off. Uses HarfBuzz for shaping, so complex scripts work correctly. Live-reloads when a font file changes.

A browser tool for variable fonts. Move the sliders and the glyph outlines update in real time. Export static instances from any point in the designspace.

Drop a font in the browser and get the full feature list plus the CSS to activate each one in a web project. Runs entirely in the browser. Made by Roel Nieskens.

Works directly with compiled binary font files for post-production work: inspecting and editing OpenType tables, reviewing GSUB and GPOS, checking kerning, running consistency checks across a type family. Runs on macOS, Windows, and Linux. Made by DTL (Dutch Type Library).

The free, open source font editor. Drawing, spacing, kerning, and OpenType feature code on Mac, Windows, and Linux. Around since 2001. The interface shows its age in places, but it's capable and free.

Full font editor for Mac and Windows. Covers the whole process: drawing, spacing, kerning, OpenType feature code, hinting, and export. Variable font support included. Ten-day free trial available.

A Python library for working with fonts programmatically. The core tool is TTX: converts a compiled font to editable XML and back to binary. The foundation of most font build infrastructure, including Google Fonts' pipeline.

A Windows font manager with OpenType feature support. The preview panel includes feature toggles and variable font axis sliders — useful when evaluating a typeface for a specific job. Windows only.

A guide to activating OpenType features in Illustrator, InDesign, Figma, Word, and CSS. Focuses on where to click and what to type, without going deep into how features work internally. Published by Pangram Pangram.

A free ebook by Simon Cozens covering font design, Unicode, and text processing. The OpenType chapters cover substitution and positioning rules, feature writing, and global scripts. Probably the best free deep-dive on the subject.

A reference for every OpenType feature tag: what it does, what order it processes in, how to access it in software, and what the code looks like. Built by Simon Cozens. More practical and approachable than the official spec.

MDN's article on using OpenType features in CSS. Covers the relevant properties with code examples you can run in the browser via the MDN Playground.

A community-maintained collection of resources for type designers. Covers learning the basics, finding tools, and the business side of running a foundry. Not specific to OpenType features, but worth knowing about if you're going further into type.