Limits

What it does not do

• Microsoft 365 and Google only. iCloud and other CalDAV calendars are not supported yet.
• Targets are main calendars. Blocks go into the main calendar of each account, not into other calendars of the account.
• Past blocks stay. The sync looks from today forward. If you delete a rule, its blocks from today on are removed. Blocks before today stay as history.
• Unverified Google app. Until Google verifies your OAuth client, Google shows a warning when someone connects a Google account.

Cloudflare free plan

The Workers Free plan allows 10 ms CPU time and 50 subrequests per invocation. slotmirror splits each sync into one step per rule direction, so that each step stays inside these limits.

The daily quotas are 100,000 Worker requests and 100,000 Durable Object requests. They cover a person or a small team. Each connected account needs a few hundred requests a day. A large team needs Workers Paid ($5 a month).

Provider rate limits

Microsoft and Google throttle a client that sends too many requests. slotmirror stays inside their limits and recovers when it is throttled.

• Outlook allows four concurrent requests per app and mailbox, and 10,000 requests in 10 minutes. One $batch already uses the four slots. All calls to a mailbox start in the Durable Object of its account, and that instance runs them one at a time.
• Google allows 600 requests per minute per user. Each call in a batch counts as one request.
• If a provider throttles, the throttled writes stay open, and the next alarm waits for Retry-After. Graph answers 429 or 503. Google answers 429, or 403 with the reason rateLimitExceeded or userRateLimitExceeded, and sends no Retry-After. Without the header, the wait is 30 seconds.
• The activity log shows the HTTP status and the error code of the provider for each failed or throttled write, for example HTTP 429 ApplicationThrottled ×13.