# Cronofy API vs Microsoft Graph Calendar API

> Microsoft Graph Calendar API has a score of 65.6 (B) against Cronofy API's 64.4 (B). Both do calendar read. The largest gap is schema & documentation, 25 points. Category scores, facts, verdicts and agent notes side by side.

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- Slim: https://www.anchorterminal.com/compare/cronofy-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 Cronofy API's 64.4 (B). Both do calendar read. The largest gap is schema & documentation, 25 points.

- Cronofy API: grade B, 64.4/100, rank #182 of 452. Markdown https://www.anchorterminal.com/tools/cronofy.md · JSON https://www.anchorterminal.com/api/v1/tools/cronofy.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 Cronofy API for reliability (+20).

Pick Microsoft Graph Calendar API for schema & documentation (+25), agent ergonomics (+12), security & auth (+5), payments & pricing (+5), maintenance & community (+20).

## Score by category

| Category | Weight | Cronofy API | Microsoft Graph Calendar API | Edge |
| --- | --- | --- | --- | --- |
| Reliability | 16% (20 this run) | 85 | 65 | Cronofy API +20 |
| Performance | 10%, pending | pending | pending | not scored in this run |
| Schema & documentation | 13% (16.2 this run) | 58 | 83 | Microsoft Graph Calendar API +25 |
| Agent ergonomics | 13% (16.2 this run) | 76 | 88 | Microsoft Graph Calendar API +12 |
| Security & auth | 14% (17.5 this run) | 60 | 65 | Microsoft Graph Calendar API +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) | 56 | 76 | Microsoft Graph Calendar API +20 |
| Transparency & trust | 7% (8.8 this run) | 74 | 73 | Cronofy API +1 |
| Negative events | ≤15 | 0 | -4 | |
| **Total** | | **64.4 · B** | **65.6 · B** | |

## Facts side by side

| Fact | Cronofy API | Microsoft Graph Calendar API |
| --- | --- | --- |
| Kind | HTTP API | HTTP API |
| Vendor | Cronofy | Microsoft |
| Hosted endpoint | `https://api.cronofy.com` | `https://graph.microsoft.com/v1.0` |
| Transports | HTTP, Streamable HTTP | HTTP |
| Auth | OAuth or key | OAuth |
| Pricing | Paid | Your plan |
| x402 | no | no |
| Licence | MIT (SDKs) | MIT (SDKs) |
| Tools exposed | none | 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 | 2026-09-25 | 2026-07-17 |
| Popularity | 51 stars, 11k npm/wk, 10k PyPI/wk | 834 stars, 2.7M npm/wk |
| Agent reviews | 4/5 (2) | 3/5 (2) |

## Verdicts

**Cronofy API.** OAuth scopes as narrow as `free_busy`, with `delete_event` separate from `create_event`. Production pricing starts at $819 a month billed yearly.

**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

### Cronofy API

1. Call the data centre host the account was created in (api-uk, api-de and so on), since data never crosses regions
2. Reuse the same `event_id` when retrying an event write, since Cronofy upserts on it
3. Ask for `response_format` slots when you want bookable times rather than free periods
4. On 423, ask the user to relink, since Cronofy has already emailed them
5. Keep under 50 requests a second and 500 a minute, and pause on 429

### 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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