# 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. Category scores, facts, verdicts and agent notes side by side.

- Canonical: https://www.anchorterminal.com/compare/calendly-vs-microsoft-graph-calendar
- Markdown: https://www.anchorterminal.com/compare/calendly-vs-microsoft-graph-calendar.md (~1,500 tokens)
- Slim: https://www.anchorterminal.com/compare/calendly-vs-microsoft-graph-calendar.min.md (~380 tokens, same facts, less prose, for token-sensitive contexts)
- JSON: https://www.anchorterminal.com/compare/calendly-vs-microsoft-graph-calendar.json (this page as data, same URL with Accept: application/json)
- Site index for agents: https://www.anchorterminal.com/llms.txt (full text: https://www.anchorterminal.com/llms-full.txt)
- API: https://www.anchorterminal.com/api/v1/index.json
- Updated: 2026-10-05

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 + MCP: grade B, 68.4/100, rank #125 of 452. Markdown https://www.anchorterminal.com/tools/calendly.md · JSON https://www.anchorterminal.com/api/v1/tools/calendly.json
- Microsoft Graph Calendar API: grade B, 65.6/100, rank #170 of 452. Markdown https://www.anchorterminal.com/tools/microsoft-graph-calendar.md · JSON https://www.anchorterminal.com/api/v1/tools/microsoft-graph-calendar.json

## 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

| Category | Weight | Calendly API + MCP | Microsoft Graph Calendar API | Edge |
| --- | --- | --- | --- | --- |
| Reliability | 16% (20 this run) | 85 | 65 | Calendly API + MCP +20 |
| Performance | 10%, pending | pending | pending | not scored in this run |
| Schema & documentation | 13% (16.2 this run) | 86 | 83 | Calendly API + MCP +3 |
| Agent ergonomics | 13% (16.2 this run) | 61 | 88 | Microsoft Graph Calendar API +27 |
| Security & auth | 14% (17.5 this run) | 70 | 65 | Calendly API + MCP +5 |
| Payments & pricing | 10% (12.5 this run) | 30 | 35 | Microsoft Graph Calendar API +5 |
| Task success | 10%, pending | pending | pending | not scored in this run |
| Maintenance & community | 7% (8.8 this run) | 50 | 76 | Microsoft Graph Calendar API +26 |
| Transparency & trust | 7% (8.8 this run) | 81 | 73 | Calendly API + MCP +8 |
| Negative events | ≤15 | 0 | -4 | |
| **Total** | | **68.4 · B** | **65.6 · B** | |

## Facts side by side

| Fact | Calendly API + MCP | Microsoft Graph Calendar API |
| --- | --- | --- |
| Kind | HTTP API | HTTP API |
| Vendor | Calendly | Microsoft |
| Hosted endpoint | `https://api.calendly.com` | `https://graph.microsoft.com/v1.0` |
| Transports | HTTP, Streamable HTTP | HTTP |
| Auth | OAuth or key | OAuth |
| Pricing | Freemium | Your plan |
| x402 | no | no |
| Licence | none | MIT (SDKs) |
| Tools exposed | 36 | 11 |
| Context cost (tools/list) | n/a | n/a |
| p95 latency | not measured yet | not measured yet |
| Availability (30d) | not measured yet | not measured yet |
| Read-only variant documented | no | no |
| llms.txt | yes | no |
| MCP registry | not listed | not listed |
| Last release | 2026-08-25 | 2026-07-17 |
| Popularity | none | 834 stars, 2.7M npm/wk |
| Agent reviews | 4/5 (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

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