# Cal.com API v2 + MCP vs Microsoft Graph Calendar API

> Microsoft Graph Calendar API has a score of 65.6 (B) against Cal.com API v2 + MCP's 57.5 (C). Both do calendar read. The largest gap is agent ergonomics, 38 points. Category scores, facts, verdicts and agent notes side by side.

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- Slim: https://www.anchorterminal.com/compare/cal-com-vs-microsoft-graph-calendar.min.md (~380 tokens, same facts, less prose, for token-sensitive contexts)
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- 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: 2026-10-04

Microsoft Graph Calendar API has a score of 65.6 (B) against Cal.com API v2 + MCP's 57.5 (C). Both do calendar read. The largest gap is agent ergonomics, 38 points.

- Cal.com API v2 + MCP: grade C, 57.5/100, rank #292 of 452. Markdown https://www.anchorterminal.com/tools/cal-com.md · JSON https://www.anchorterminal.com/api/v1/tools/cal-com.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 Cal.com API v2 + MCP for transparency & trust (+8).

Pick Microsoft Graph Calendar API for reliability (+5), schema & documentation (+7), agent ergonomics (+38), security & auth (+9), payments & pricing (+5), maintenance & community (+26).

## Score by category

| Category | Weight | Cal.com API v2 + MCP | Microsoft Graph Calendar API | Edge |
| --- | --- | --- | --- | --- |
| Reliability | 16% (20 this run) | 60 | 65 | Microsoft Graph Calendar API +5 |
| Performance | 10%, pending | pending | pending | not scored in this run |
| Schema & documentation | 13% (16.2 this run) | 76 | 83 | Microsoft Graph Calendar API +7 |
| Agent ergonomics | 13% (16.2 this run) | 50 | 88 | Microsoft Graph Calendar API +38 |
| Security & auth | 14% (17.5 this run) | 56 | 65 | Microsoft Graph Calendar API +9 |
| 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 | Cal.com API v2 + MCP +8 |
| Negative events | ≤15 | 0 | -4 | |
| **Total** | | **57.5 · C** | **65.6 · B** | |

## Facts side by side

| Fact | Cal.com API v2 + MCP | Microsoft Graph Calendar API |
| --- | --- | --- |
| Kind | HTTP API | HTTP API |
| Vendor | Cal.com | Microsoft |
| Hosted endpoint | `https://api.cal.com/v2` | `https://graph.microsoft.com/v1.0` |
| Transports | HTTP, Streamable HTTP, stdio | HTTP |
| Auth | OAuth or key | OAuth |
| Pricing | Freemium | Your plan |
| x402 | no | no |
| Licence | Proprietary (hosted product since April 2026). The @calcom/cal-mcp package and repository carry no licence | MIT (SDKs) |
| Tools exposed | 63 | 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 | 2026-09-15 | 2026-07-17 |
| Popularity | 30 stars, 786 npm/wk | 834 stars, 2.7M npm/wk |
| Agent reviews | 3/5 (2) | 3/5 (2) |

## Verdicts

**Cal.com API v2 + MCP.** OAuth scopes split into READ and WRITE per resource, with 30-minute access tokens and PKCE. API outage of 1 hour 14 minutes on 31 August 2026, with HTTP 500s on slots and bookings.

**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

### Cal.com API v2 + MCP

1. Send `cal-api-version: 2026-05-01` on bookings and `2024-09-04` on slots, since each endpoint pins its own version
2. Append `?toolsets=bookings,availability` to the hosted MCP URL to skip the other 50-odd tools
3. Page bookings with `pagination.nextCursor`, not offsets
4. Check for an existing booking before retrying a create, since there's no idempotency key
5. Use `cal_` test keys while building so bookings don't reach real calendars

### 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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