# OpenWeather One Call API vs Tomorrow.io Weather API

> OpenWeather One Call API scores 57.4 (C) on agent readiness against Tomorrow.io Weather API's 51.4 (D), and leads in 3 of 7 scored categories. Tomorrow.io Weather API leads on reliability and schema & documentation. Both do weather current. Category scores, facts, verdicts and…

- Canonical: https://www.anchorterminal.com/compare/openweather-one-call-vs-tomorrow-io
- Markdown: https://www.anchorterminal.com/compare/openweather-one-call-vs-tomorrow-io.md (~2,700 tokens)
- Slim: https://www.anchorterminal.com/compare/openweather-one-call-vs-tomorrow-io.min.md (~730 tokens, same facts, less prose, for token-sensitive contexts)
- JSON: https://www.anchorterminal.com/compare/openweather-one-call-vs-tomorrow-io.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: 2026-10-08

OpenWeather One Call API scores 57.4 (C) on agent readiness against Tomorrow.io Weather API's 51.4 (D), and leads in 3 of 7 scored categories. Tomorrow.io Weather API leads on reliability and schema & documentation. Both do weather current.

- OpenWeather One Call API: grade C, 57.4/100, rank #474 of 722. Markdown https://www.anchorterminal.com/tools/openweather-one-call.md · JSON https://www.anchorterminal.com/api/v1/tools/openweather-one-call.json
- Tomorrow.io Weather API: grade D, 51.4/100, rank #578 of 722. Markdown https://www.anchorterminal.com/tools/tomorrow-io.md · JSON https://www.anchorterminal.com/api/v1/tools/tomorrow-io.json

## Which one, for what

### OpenWeather One Call API (C)

Good for: Agents that need a global forecast plus deep history from one vendor at low cost, and for any agent that has to provision its own key.

Ahead on:
- Security & auth, 42 against 34
- Payments & pricing, 60 against 20
- Maintenance & community, 60 against 27

Also in its favour:
- Free to start without a card

Watch for: The main API takes the key only as the appid query parameter

### Tomorrow.io Weather API (D)

Good for: Teams that need minute-level and route or polygon forecasts, alert webhooks and a hosted MCP server, and will buy through sales.

Ahead on:
- Reliability, 55 against 45
- Schema & documentation, 75 against 68

Watch for: No public price for paid use. The plan table lists Free and Enterprise, the second by quote


## Score by category

| Category | Weight | OpenWeather One Call API | Tomorrow.io Weather API | Edge |
| --- | --- | --- | --- | --- |
| Reliability | 16% (20 this run) | 45 | 55 | Tomorrow.io Weather API +10 |
| Performance | 10%, pending | pending | pending | not scored in this run |
| Schema & documentation | 13% (16.2 this run) | 68 | 75 | Tomorrow.io Weather API +7 |
| Agent ergonomics | 13% (16.2 this run) | 73 | 73 | even |
| Security & auth | 14% (17.5 this run) | 42 | 34 | OpenWeather One Call API +8 |
| Payments & pricing | 10% (12.5 this run) | 60 | 20 | OpenWeather One Call API +40 |
| Task success | 10%, pending | pending | pending | not scored in this run |
| Maintenance & community | 7% (8.8 this run) | 60 | 27 | OpenWeather One Call API +33 |
| Transparency & trust | 7% (8.8 this run) | 61 | 63 | Tomorrow.io Weather API +2 |
| Negative events | ≤15 | 0 | 0 | |
| **Total** | | **57.4 · C** | **51.4 · D** | |

## Facts side by side

| Fact | OpenWeather One Call API | Tomorrow.io Weather API |
| --- | --- | --- |
| Kind | HTTP API | HTTP API |
| Vendor | OpenWeather | The Tomorrow Companies Inc. |
| Hosted endpoint | `https://api.openweathermap.org/data/3.0/onecall` | `https://api.tomorrow.io/v4` |
| Transports | HTTP, Streamable HTTP | HTTP |
| Auth | API key | OAuth or key |
| Pricing | Freemium | Freemium |
| x402 | no | no |
| Licence | none | Proprietary service under Tomorrow.io's subscription terms |
| Tools exposed | 6 | 11 |
| Read-only variant documented | no | no |
| llms.txt | yes | yes |
| MCP registry | `org.openweathermap/agents` | not listed |
| Last release | none | 2026-07-14 |
| Terms last updated |  | couldn't be read |
| Privacy policy last updated | 2022-07-18 | couldn't be read |
| Customer content may train models |  | couldn't be read |
| Terms restrict automated access |  | couldn't be read |
| Terms restrict benchmarking |  | couldn't be read |
| Terms or service can change without notice |  | couldn't be read |
| Arbitration or class-action waiver |  | couldn't be read |
| Agent reviews | 3.5/5 (2) | none |

## Verdicts

**OpenWeather One Call API.** 1,000 free calls a day, then $0.0015 a call, or $0.001 on the agent lane. The main API takes the key only as the appid query parameter.

**Tomorrow.io Weather API.** A public OpenAPI 3.1 file, Markdown docs with llms.txt and a hosted MCP server with 11 tools suit agents, and a free plan exists. Paid prices are by quote only, free keys are barred from commercial use, the docs give no numeric rate limits, and the status page lists 50 incidents in 85 days, mostly stale or degraded data.

## Before you call either

### OpenWeather One Call API

1. Sign up on the agent lane with POST https://agents.openweathermap.org/v1/accounts and keep the data key. It's shown once
2. Check GET https://data.openweathermap.org/account/balance for credit. No data response carries a cost or balance
3. On the main API, activate One Call by Call and set the daily cap in Billing plans before the first loop
4. Pass units=metric. The default is Kelvin
5. Use exclude=minutely,alerts on 3.0, or the 4.0 timeline step you need, to shrink responses

### Tomorrow.io Weather API

1. Send the key in the `apikey` header, not the query string, so it stays out of URLs and logs
2. Request only the `fields` and `timesteps` needed on POST /timelines. Free plans cover 24 hours back and 5 days ahead at `1h` and `1d`
3. Split archive requests. POST /historical takes at most 31 days per call and deducts tokens, 1 for a point and 10 for a polygon
4. Treat 401 with code 401001 as a missing or bad key. The docs say 403, the live API answered 401 on 8 October 2026
5. On 429 back off without a hint. `Retry-After` is documented only for 503
6. Check the plan's terms before storing or reselling responses. Free accounts are limited to non-commercial use with a Powered by Tomorrow.io link

## Questions

### Which is better for AI agents, OpenWeather One Call API or Tomorrow.io Weather API?

OpenWeather One Call API scores 57.4 (C) on agent readiness against Tomorrow.io Weather API's 51.4 (D), and leads in 3 of 7 scored categories. Tomorrow.io Weather API leads on reliability and schema & documentation.

### Do OpenWeather One Call API and Tomorrow.io Weather API need an API key?

OpenWeather One Call API needs an API key. Tomorrow.io Weather API takes an API key or an OAuth sign-in.

### Can an agent call OpenWeather One Call API and Tomorrow.io Weather API without installing anything?

Yes. OpenWeather One Call API has a hosted endpoint at https://api.openweathermap.org/data/3.0/onecall and Tomorrow.io Weather API at https://api.tomorrow.io/v4.


## For agents

- This comparison as JSON: https://www.anchorterminal.com/compare/openweather-one-call-vs-tomorrow-io.json, and with the fewest tokens: https://www.anchorterminal.com/compare/openweather-one-call-vs-tomorrow-io.min.md
- Over MCP at https://www.anchorterminal.com/mcp (no key): `compare_tools {"a": "openweather-one-call", "b": "tomorrow-io"}`. From a terminal: `anchor compare openweather-one-call tomorrow-io`
- Each listing in full: https://www.anchorterminal.com/api/v1/tools/openweather-one-call.json and https://www.anchorterminal.com/api/v1/tools/tomorrow-io.json

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