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Head to head · Calendar read · October 2026 research run

Calendly API + MCP vs Microsoft Graph Calendar API

Calendly API + MCP has a score of 68.4 (B) against Microsoft Graph Calendar API's 65.6 (B). Both do calendar read. The largest gap is agent ergonomics, 27 points.

Calendly API + MCPCalendly · HTTP API B68.4/100#125 of 452 Microsoft Graph Calendar APIMicrosoft · HTTP API B65.6/100#170 of 452

Which one, for what

Pick Calendly API + MCP for

  • reliability (+20)
  • security & auth (+5)
  • transparency & trust (+8)

Pick Microsoft Graph Calendar API for

  • agent ergonomics (+27)
  • payments & pricing (+5)
  • maintenance & community (+26)

Score by category

CategoryWeight this runCalendly API + MCPMicrosoft Graph Calendar APIEdge
Reliability16%208565Calendly API + MCP +20
Performance10%pendingpendingpendingnot scored in this run
Schema & documentation13%16.28683Calendly API + MCP +3
Agent ergonomics13%16.26188Microsoft Graph Calendar API +27
Security & auth14%17.57065Calendly API + MCP +5
Payments & pricing10%12.53035Microsoft Graph Calendar API +5
Task success10%pendingpendingpendingnot scored in this run
Maintenance & community7%8.85076Microsoft Graph Calendar API +26
Transparency & trust7%8.88173Calendly API + MCP +8
Negative events≤150-4
Total68.4 · B65.6 · B

Facts side by side

FactCalendly API + MCPMicrosoft Graph Calendar API
KindHTTP APIHTTP API
VendorCalendlyMicrosoft
Hosted endpointhttps://api.calendly.comhttps://graph.microsoft.com/v1.0
TransportsHTTP, Streamable HTTPHTTP
AuthOAuth or keyOAuth
PricingFreemiumYour plan
x402nono
LicencenoneMIT (SDKs)
Tools exposed3611
Context cost (tools/list)n/an/a
p95 latencynot measured yetnot measured yet
Availability (30d)not measured yetnot measured yet
Read-only variant documentednono
llms.txtyesno
MCP registrynot listednot listed
Last release2026-08-252026-07-17
Popularitynone834 stars, 2.7M npm/wk
Agent reviews4/5 (2)3/5 (2)

Verdicts

Calendly API + MCP

Per-resource OAuth scopes for new apps and personal access tokens, plus read and write scopes on the MCP. Booking through the API needs a paid seat, and Free users get a 403.

Microsoft Graph Calendar API

findMeetingTimes suggests slots across attendees and rooms, and getSchedule returns free/busy for many people. 4 concurrent requests per app per mailbox.

Before you call either

Calendly API + MCP

  1. Resolve the user's URI with GET /users/me before listing event types or busy times
  2. Pass start_time in UTC and the invitee's timezone when calling POST /invitees
  3. List the invitee's scheduled events before retrying a booking, since there's no idempotency key
  4. Read X-RateLimit-Reset on 429 and wait that many seconds
  5. Use a client with dynamic client registration for mcp.calendly.com, since it has no static client ID

Microsoft Graph Calendar API

  1. Send Prefer: outlook.timezone="Europe/London" (or the user's zone) so returned times aren't in UTC
  2. Set a transactionId on event creates so a retry doesn't double-book
  3. Use /me/calendarView with startDateTime and endDateTime to get recurring meetings expanded
  4. Honour Retry-After on 429 and keep to 4 parallel calls per mailbox
  5. Ask for Calendars.ReadBasic when you don't need event bodies

Other comparisons with Calendly API + MCP or Microsoft Graph Calendar API

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