Note: this article is mostly for internal Relm developers running unreleased builds of the Excel add-in against a local dev server. Production users on macOS who installed from AppSource don't need any of this.
If you're running an Excel add-in dev build that loads from localhost:3100, macOS's TLS validation may refuse to connect to the dev server until you trust the localhost certificate.
Symptoms
- The Relm taskpane in Excel for Mac shows a blank panel or a "couldn't load" error.
- The browser dev console (when remote-debugging the taskpane via Safari Web Inspector) shows a certificate-trust failure for
https://localhost:3100.
Fix
- Open Safari (yes, even if you don't use it) and visit
https://localhost:3100. - Safari prompts that the certificate is untrusted. Click Show Details → Visit this website.
- Confirm at the macOS keychain prompt — enter your login password.
- Open Keychain Access. Find the
localhostcertificate. - Right-click → Get Info → Trust → When using this certificate: Always Trust.
- Close Keychain Access (you'll be prompted to authenticate; do so).
- Restart Excel.
The taskpane should now load.
Why this is needed
Office Add-ins on Mac use a WebKit web view that consults the macOS keychain for TLS trust decisions. The dev server's self-signed certificate isn't trusted by default. The fix above teaches the keychain to trust it.
Production builds
In production, the add-in loads from excel-plugin.relm.ai — a real, publicly-trusted Let's Encrypt certificate. macOS trusts that out of the box.