multi-post

Write a post once, then send it to Bluesky, LinkedIn, Mastodon and X.

Live at https://multi-post.cattell.com. Every push to main deploys it.

• @mentions that work everywhere. Type @, find the person on each platform once, and their profiles are saved. Next time, @ plus a few letters is enough.
• Images. Up to 4 per post, each with alt text.
• Direct posting to all four platforms, once you connect your accounts.
• Hosted on Cloudflare (free plan). Sign in with Google or GitHub.

It is built for one person, or a few who share the same social accounts. Only the email addresses you list can sign in.

Deploy to Cloudflare

You need Node.js 22.13 or newer and a Cloudflare account.

1. Install the tools and sign in:

   npm install

   npx wrangler login

2. Create the database. Copy the database_id it prints into wrangler.jsonc.

   npx wrangler d1 create multi-post

3. Set who may sign in, and a long random secret (for example the output of openssl rand -hex 32). The secret signs your login and encrypts the account tokens the app stores.

   npx wrangler secret put ALLOWED_EMAILS

   npx wrangler secret put SESSION_SECRET

   ALLOWED_EMAILS is one or more email addresses, separated by commas. Use the address on your Google or GitHub account.

4. Deploy. This also creates the database tables.

   npm run deploy

   Wrangler prints the address, like https://multi-post.<you>.workers.dev.

5. Set up sign-in (next section), then deploy once more.

Your own domain: set the routes line in wrangler.jsonc to the name you want and deploy again. The domain must already be on your Cloudflare account.

Automatic image descriptions (optional)

When you attach an image, the app can suggest alt text for it using Claude and put it in the description box, marked "Suggested automatically" so you know to check it. It never replaces anything you have typed. The image and the post's text are sent to Anthropic to write the description.

1. Create an API key in the Claude Console, and set a monthly spend limit for it.

2. Save it:

   npx wrangler secret put ANTHROPIC_API_KEY

3. Deploy again.

It uses Claude Opus 5.5, which costs roughly 1p per image or less. To use another model, set ALT_TEXT_MODEL (for example claude-haiku-5-5, which is much cheaper) as a variable in wrangler.jsonc or the Cloudflare dashboard. Without a key, the description box works as before.

Set up sign-in

Set up Google, GitHub, or both. The sign-in page shows a button for each one you set up. YOUR-APP-ADDRESS is the address from step 4, or your own domain.

Google

1. In the Google Cloud console, create a project, then Create credentials → OAuth client ID, type Web application. (It may ask you to fill in a consent screen first.)

2. Add the authorised redirect URI https://YOUR-APP-ADDRESS/api/login/google/callback.

3. Save the client ID and secret:

   npx wrangler secret put GOOGLE_CLIENT_ID

   npx wrangler secret put GOOGLE_CLIENT_SECRET

GitHub

1. In GitHub: Settings → Developer settings → OAuth Apps → New OAuth App.

2. Set the authorization callback URL to https://YOUR-APP-ADDRESS/api/login/github/callback.

3. Generate a client secret, then save both values:

   npx wrangler secret put GITHUB_CLIENT_ID

   npx wrangler secret put GITHUB_CLIENT_SECRET

Your GitHub account must have a verified email that is in ALLOWED_EMAILS. It does not need to be public.

Who gets in

Only verified email addresses in ALLOWED_EMAILS. Everyone who signs in shares the same saved people and connected accounts. Removing an address locks that person out straight away. A sign-in lasts 30 days.

Connect your accounts

Open the app, sign in, and use Your accounts. A platform that is not connected still works: you get a Copy text and open link to its own composer.

Bluesky

Click Connect and enter your handle and an app password (Bluesky → Settings → Privacy and security → App passwords).

Mastodon

On your server: Preferences → Development → New application. Tick write:statuses, write:media and read:search. Click Connect and paste the server name and the access token.

X

X charges for API use. Check their current pricing first.

1. At developer.x.com, create a project and app.

2. Under User authentication settings: enable OAuth 2.0, type Web App, permissions Read and write.

3. Set the callback URL to https://YOUR-APP-ADDRESS/api/callback/x.

4. Save the client ID and secret, then deploy again:

   npx wrangler secret put X_CLIENT_ID

   npx wrangler secret put X_CLIENT_SECRET

5. In the app, click Connect next to X.

LinkedIn

1. At linkedin.com/developers, create an app. LinkedIn asks you to link it to a company page.

2. On the Products tab, add Share on LinkedIn and Sign In with LinkedIn using OpenID Connect.

3. On the Auth tab, add the redirect URL https://YOUR-APP-ADDRESS/api/callback/linkedin.

4. Save the client ID and secret:

   npx wrangler secret put LINKEDIN_CLIENT_ID

   npx wrangler secret put LINKEDIN_CLIENT_SECRET

5. In the app, click Connect next to LinkedIn. LinkedIn sign-ins last about 60 days; the app shows how long is left.

How mentions work

1. Type @ and a name in the post box.
2. Pick a saved person, or choose Find "name" on all platforms…
3. Pick their profile on each platform (skip any they are not on) and save.
4. The draft shows @[Jane Doe]. The preview shows what each platform gets:

Platform	Becomes	How the profile is found
Bluesky	@jane.bsky.social (a real, linked mention)	Live search by name or handle
Mastodon	@jane@server.social	Live search, or exact lookup of user@server
X	@janedoe	You type the handle. It is checked when X is connected
LinkedIn	Jane Doe (plain name)	You paste the profile link

If someone has no profile on a platform, their plain name is used there.

Limits to know about

• LinkedIn mentions are plain text. LinkedIn gives no way to look people up, and only links a name picked inside LinkedIn itself.
• X has no name search on its standard API, so handles are typed by hand.
• Images larger than about 1 MB are shrunk in your browser to fit Bluesky's limit. WebP and other formats are converted to JPEG. Large animated GIFs lose their animation.
• Copy-and-open links cannot carry images. Add them by hand there.

Develop

cp .dev.vars.example .dev.vars

npm run dev

This runs the app at http://localhost:8787 with a local database. To sign in locally, add http://localhost:8787/api/login/google/callback (or the GitHub one) as a second redirect URL on your sign-in app. npm run dev:node does the same on plain Node, without Cloudflare's tooling.

npm test

• src/worker.js – the API
• src/login.js – Google and GitHub sign-in
• src/accounts.js – connecting and storing your accounts
• src/resolve.js – profile lookup per platform
• src/post.js – posting, with images
• src/db.js – saved people and profiles
• src/auth.js – signed cookies and encryption
• public/ – the page; public/render.js turns @[Name] into each platform's text and is shared with the Worker
• migrations/ – database tables