A single-user bridge service that automatically cross-posts from your Bluesky account to your Mastodon account. Built specifically for Val.town with TypeScript and Deno.
- Connects your accounts: Securely links your Bluesky and Mastodon accounts using OAuth
- Automatic syncing: Checks for new Bluesky posts every 15 minutes and cross-posts them to Mastodon
- Smart filtering: Only syncs regular posts, not replies, reposts, or posts that start with mentions, so hopefully only content that makes sense in the Mastodon context
- Smart transformations: Converts Bluesky mentions (@handle.bsky.social) to profile links since they don't exist on Mastodon
- Media support: Uploads images and videos from Bluesky to your Mastodon instance
- Duplicate prevention: Tracks synced posts to avoid posting the same content twice
- Error handling: Retries failed posts and logs errors for troubleshooting
✅ OAuth authentication for both Bluesky and Mastodon
✅ Media cross-posting (images & videos)
✅ Mention transformation (handles → profile links)
✅ Duplicate prevention via content hashing
✅ Retry mechanism with exponential backoff
✅ Error logging and sync tracking
✅ Setup wizard for easy configuration
Just clone my https://www.val.town/x/tijs/atproto-to-fediverse val
HTTP Trigger (for the web interface and API):
- Set
backend/index.tsas an HTTP val - This serves the setup wizard and handles OAuth callbacks
Cron Trigger (for automatic syncing):
- Set
cronjob.tsas a Cron val - Schedule:
*/15 * * * *(every 15 minutes) - For paid accounts, you can use shorter intervals like
*/5 * * * *(every 5 minutes)
Set these environment variables in your Val.town account:
# Your Val.town deployment URL
VALTOWN_URL=https://your-val-url.web.val.run
# Bluesky App Password for sync service (services do not work with oauth yet on bsky)
ATPROTO_APP_PASSWORD=your-bluesky-app-password
# Security: restrict login to specific handle only
ATPROTO_ALLOWED_HANDLE=your.handle.bsky.social- Go to Bluesky Settings > App Passwords
- Create a new App Password (name it something like "Bridge Service")
- Copy the generated password and set it as
ATPROTO_APP_PASSWORD
The ATPROTO_ALLOWED_HANDLE variable restricts OAuth setup to only your Bluesky
handle, preventing others from hijacking your single-user bridge service.
The OAuth client metadata is automatically generated based on your VALTOWN_URL
environment variable. No manual configuration is needed!
The client metadata will be available at:
https://your-val-url.web.val.run/client
The service automatically registers with your Mastodon instance during setup - no manual configuration needed.
- Visit your HTTP val URL (e.g.,
https://your-val-url.web.val.run) - Check the Setup Status: The landing page shows a checklist of what environment variables need to be configured
- Configure missing variables: Set any missing environment variables in your Val.town settings
- Click "Get Started" to begin the setup wizard once all required variables are set
- Connect your Bluesky account by entering your handle
- Connect your Mastodon account by entering your instance URL
- Complete the setup - that's all!
Once configured, the service runs automatically:
- Every 15 minutes (or your configured interval), the cron job runs
- It fetches new posts from your Bluesky account
- Transforms the content (mentions become profile links)
- Uploads any media to your Mastodon instance
- Creates the cross-post on Mastodon
- Logs the result for your review
✅ Included:
- Regular posts with text
- Posts with images/videos
- Posts with links and hashtags
- Posts with mentions (converted to profile links)
❌ Excluded:
- Replies to other posts
- Posts that start with mentions (e.g., "@handle.bsky.social blah blah") - these are typically conversation starters
- Empty posts
- Posts you've already cross-posted
- Re-posts (posts that embed another post)
- Connection Status: See which accounts are connected
- Sync Controls: Enable/disable auto-sync and trigger manual syncs
- Recent Activity: View recently synced posts and their status
- Error Logs: Track sync failures and troubleshoot issues
- Disconnect Options: Disconnect individual accounts if needed
Visit your val's dashboard to see:
- Setup status and account connections
- Recent sync activity and statistics
- Error logs for troubleshooting
- Post sync history
- Free Val.town accounts: 15-minute minimum sync interval
- Bluesky media limits: 1MB images, 100MB videos
- Mastodon compatibility: Works with all Mastodon instances
- Single user: Designed for personal use (one Bluesky → one Mastodon)
Setup issues: Check the setup status checklist on the landing page for
missing environment variables
OAuth failures: Ensure your VALTOWN_URL is publicly accessible (client
metadata is auto-generated at /client)
"Unauthorized" errors: Verify ATPROTO_ALLOWED_HANDLE matches your exact
Bluesky handle
App Password errors: Generate a new App Password in Bluesky settings and
update ATPROTO_APP_PASSWORD
Sync not working: Verify both accounts are connected in the dashboard
Missing posts: Check the sync logs for specific error messages
Media upload fails: Bluesky/Mastodon may have different file size limits
- All tokens are stored securely in SQLite
- No data leaves your Val.town instance
- OAuth follows security best practices (PKCE, DPoP)
- Single-user security:
ATPROTO_ALLOWED_HANDLErestricts access to your handle only - App Password option: More reliable than OAuth tokens for automated services
- You can disconnect accounts anytime from the dashboard
- Single-user architecture prevents data mixing
This is an open-source project. For issues or feature requests, check the repository or Val.town community forums.