ᛃ epos

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Overview ​

Epos (ἔπος, “epic story”; pronounced EH-poss) is an opinionated engine for building Chromium browser extensions with React.

While frameworks like WXT and Plasmo prioritize flexibility, Epos focuses on a zero-config experience with powerful features that work out of the box.

Installation ​

Epos is not an npm package. Instead, the engine is a browser extension installed from the Chrome Web Store. In other words, Epos is an extension for building other extensions.

Workflow ​

Once installed, the workflow is straightforward:

  1. Connect: Link your local project folder to Epos.
  2. Develop: Epos runs your code directly in the browser.
  3. Export: Ready to ship? Click the Export button to get a standalone ZIP file.

Philosophy ​

Epos is not a universal framework. It focuses on a specific tech stack to reduce setup and complexity.

The engine rethinks how extensions are built, making trade-offs that allow a smoother developer experience and powerful built-in features.

Epos prioritizes ease of use for the most common use cases, even if that means giving up some flexibility.

What You Get ​

At a high level, Epos gives you:

  • A cross-context messaging system.
  • Shared state with persistence and sync.
  • Storage for files and other data.
  • Extension APIs available in any context.
  • Automatic script injection + Shadow DOM.
  • A simpler setup through epos.json.

Core Constraints ​

  • React: Epos is built around React.
  • Chromium: Firefox and Safari are not supported.
  • Manifest V3: No support for the legacy Manifest V2.
  • No HMR: Live reload is available, but hot module replacement is not.
  • No Source Maps: Epos injects its runtime into your code, so source maps do not work.
  • Permissions: Certain manifest permissions are required and cannot be omitted.

These constraints are intentional trade-offs that make Epos's features possible. You can learn more about them in the Features section.

Is It for You? ​

Epos fits best if you want to build a Chromium extension with React. The engine gives you a powerful toolset with minimal setup. It has reasonable defaults for most use cases and can be customized when needed.

However, if you need support for non-Chromium browsers, require specific Chrome APIs, or want full manual control over configuration, Epos might not be the right choice.