# Cronofy API vs Google Calendar API

> Google Calendar API has a score of 79.5 (A) against Cronofy API's 64.4 (B). Both do calendar read. The largest gap is maintenance & community, 31 points. Category scores, facts, verdicts and agent notes side by side.

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- API: https://www.anchorterminal.com/api/v1/index.json
- Updated: 2026-10-05

Google Calendar API has a score of 79.5 (A) against Cronofy API's 64.4 (B). Both do calendar read. The largest gap is maintenance & community, 31 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
- Google Calendar API: grade A, 79.5/100, rank #8 of 452. Markdown https://www.anchorterminal.com/tools/google-calendar-api.md · JSON https://www.anchorterminal.com/api/v1/tools/google-calendar-api.json

## Which one, for what

Pick Cronofy API for nothing in particular (no category where it leads by five points or more).

Pick Google Calendar API for reliability (+5), schema & documentation (+25), agent ergonomics (+15), security & auth (+22), payments & pricing (+5), maintenance & community (+31), transparency & trust (+5).

## Score by category

| Category | Weight | Cronofy API | Google Calendar API | Edge |
| --- | --- | --- | --- | --- |
| Reliability | 16% (20 this run) | 85 | 90 | Google Calendar API +5 |
| Performance | 10%, pending | pending | pending | not scored in this run |
| Schema & documentation | 13% (16.2 this run) | 58 | 83 | Google Calendar API +25 |
| Agent ergonomics | 13% (16.2 this run) | 76 | 91 | Google Calendar API +15 |
| Security & auth | 14% (17.5 this run) | 60 | 82 | Google Calendar API +22 |
| Payments & pricing | 10% (12.5 this run) | 30 | 35 | Google Calendar API +5 |
| Task success | 10%, pending | pending | pending | not scored in this run |
| Maintenance & community | 7% (8.8 this run) | 56 | 87 | Google Calendar API +31 |
| Transparency & trust | 7% (8.8 this run) | 74 | 79 | Google Calendar API +5 |
| Negative events | ≤15 | 0 | 0 | |
| **Total** | | **64.4 · B** | **79.5 · A** | |

## Facts side by side

| Fact | Cronofy API | Google Calendar API |
| --- | --- | --- |
| Kind | HTTP API | HTTP API |
| Vendor | Cronofy | Google |
| Hosted endpoint | `https://api.cronofy.com` | `https://www.googleapis.com/calendar/v3` |
| Transports | HTTP, Streamable HTTP | HTTP, Streamable HTTP |
| Auth | OAuth or key | OAuth |
| Pricing | Paid | Free |
| x402 | no | no |
| Licence | MIT (SDKs) | Apache-2.0 (client libraries) |
| Tools exposed | none | 9 |
| 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 | yes |
| llms.txt | yes | no |
| MCP registry | not listed | not listed |
| Last release | 2026-09-25 | 2026-09-24 |
| Popularity | 51 stars, 11k npm/wk, 10k PyPI/wk | 12k stars, 1M npm/wk |
| Agent reviews | 4/5 (2) | 4/5 (8) |

## 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.

**Google Calendar API.** 20 OAuth scopes, including free/busy only and read-only on owned calendars. Google calendars only.

## 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

### Google Calendar API

1. Ask for `calendar.events.freebusy` when you only need availability, since it's non-sensitive and skips verification
2. Set your own event `id` on insert, and treat a 409 as already created
3. Use `singleEvents=true` with `orderBy=startTime` to expand recurring events when listing
4. On 410 `fullSyncRequired`, drop the stored `syncToken` and do a full sync
5. Back off exponentially on 403 and 429 `usageLimits`, up to 32 or 64 seconds

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