Substack Reader Switcher

One click to flip any Substack post between the publication webpage and the built-in reader (audio player) — in both directions.

A tiny cross-browser extension that adds a floating pill button in the corner of every Substack post:

You are on…	Button says	Takes you to…
A publication's webpage (example.substack.com/p/… or a custom domain like thefp.com/p/…)	🎧 Switch to Post	The built-in reader at substack.com/home/post/p-{id} — with Substack's audio player
The built-in reader on substack.com (/home/post/p-{id}, /@user/p-{id}, /inbox/post/{id})	🌐 Switch to Webpage	The post's original publication webpage

No account, no permission dialogs, no data collection, no tracking. It only reads the current page and, when needed, calls Substack's own public API.

Install

⬇ Download the latest release ZIP (under Assets, grab substack-reader-switcher-*.zip), then extract it — you get a folder with the extension files. No git or command line needed.

Chrome / Edge / Brave / Opera / Vivaldi (any Chromium browser)

1. Open chrome://extensions (or edge://extensions, etc.).
2. Enable Developer mode (toggle in the corner).
3. Click Load unpacked and select the extracted folder.

Don't delete the folder afterwards — the browser loads the extension from it.

Firefox (109+)

Temporary install (resets when Firefox restarts):

1. Open about:debugging#/runtime/this-firefox.
2. Click Load Temporary Add-on… and select manifest.json inside the extracted folder.

For a permanent install the extension must be signed — zip the folder contents and submit it to addons.mozilla.org (self-distribution signing is free), or use Firefox Developer Edition with xpinstall.signatures.required set to false.

Note

In Firefox, MV3 extensions don't get site access automatically. After installing, open the extension's entry in about:addons → Permissions and allow access to the sites you read Substack on (or allow on all sites).

Safari (16.4+)

Safari can't load web extensions directly; convert with Apple's tool on macOS:

xcrun safari-web-extension-converter "path/to/extracted/folder"

Then run the generated Xcode project and enable the extension in Safari's settings. The code itself needs no changes.

How it works

• Webpage → reader: the post's numeric ID is extracted from the page (app-link meta tags, the __NEXT_DATA__ blob, or inline scripts), falling back to the publication's own /api/v1/posts/{slug} endpoint. The button links to https://substack.com/home/post/p-{id}.
• Reader → webpage: the post ID is parsed from the URL, and the original article URL comes from https://substack.com/api/v1/posts/by-id/{id} (post.canonical_url), with the server-rendered <link rel="canonical"> used as a no-network fast path when it's trustworthy.
• SPA-aware: substack.com is a single-page app, so the script watches for client-side URL changes and adds/removes/updates the button accordingly.

It's a pure content script — no background worker, no chrome.* APIs, no stored data — which is what keeps it compatible across every browser with a single codebase.

Files

File	Purpose
manifest.json	MV3 manifest (content script registration, Firefox settings)
content.js	All logic: page detection, post-ID/URL resolution, button injection
styles.css	Floating button styling
Example Links.txt	Sample post/reader URL pairs for manual testing
CLAUDE.md	Developer/AI-agent context notes

Limitations

• Substack posts on custom domains are matched via the broad *://*/p/* pattern; the script immediately exits on non-Substack pages, but the content script does load there.
• If Substack changes its URL formats or API responses, detection may need updating (see CLAUDE.md for the current assumptions).

License

MIT