# OpenWeather One Call API vs Stormglass API

> OpenWeather One Call scores 57.4 (C) to Stormglass's 39.9 (E) for weather forecasts. Prices, MCP, x402, uptime and agent notes side by side.

- Canonical: https://www.anchorterminal.com/compare/openweather-one-call-vs-stormglass
- Markdown: https://www.anchorterminal.com/compare/openweather-one-call-vs-stormglass.md (~2,750 tokens)
- Slim: https://www.anchorterminal.com/compare/openweather-one-call-vs-stormglass.min.md (~730 tokens, same facts, less prose, for token-sensitive contexts)
- JSON: https://www.anchorterminal.com/compare/openweather-one-call-vs-stormglass.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: 2026-10-09

OpenWeather One Call API scores 57.4 (C) on agent readiness against Stormglass API's 39.9 (E), and leads in 6 of 7 scored categories. Both do weather forecasts.

- OpenWeather One Call API: grade C, 57.4/100, rank #608 of 950. Markdown https://www.anchorterminal.com/tools/openweather-one-call.md · JSON https://www.anchorterminal.com/api/v1/tools/openweather-one-call.json
- Stormglass API: grade E, 39.9/100, rank #914 of 950. Markdown https://www.anchorterminal.com/tools/stormglass.md · JSON https://www.anchorterminal.com/api/v1/tools/stormglass.json
- Best weather and climate data APIs for AI agents: https://www.anchorterminal.com/best/weather/index.md
- All 120 weather comparisons: https://www.anchorterminal.com/compare/weather/index.md

## 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:
- Reliability, 45 against 34
- Schema & documentation, 68 against 40
- Agent ergonomics, 73 against 65
- Payments & pricing, 60 against 25
- Maintenance & community, 60 against 15
- Transparency & trust, 61 against 45

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

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

### Stormglass API (E)

Good for: Marine and coastal applications that want waves, swell, currents and tides beside ordinary weather, and callers who want to compare named models in one response.

Watch for: No OpenAPI file, llms.txt, official SDK or changelog was found. The docs are eleven Markdown pages


## Score by category

| Category | Weight | OpenWeather One Call API | Stormglass API | Edge |
| --- | --- | --- | --- | --- |
| Reliability | 16% (20 this run) | 45 | 34 | OpenWeather One Call API +11 |
| Performance | 10%, pending | pending | pending | not scored in this run |
| Schema & documentation | 13% (16.2 this run) | 68 | 40 | OpenWeather One Call API +28 |
| Agent ergonomics | 13% (16.2 this run) | 73 | 65 | OpenWeather One Call API +8 |
| Security & auth | 14% (17.5 this run) | 42 | 44 | Stormglass API +2 |
| Payments & pricing | 10% (12.5 this run) | 60 | 25 | OpenWeather One Call API +35 |
| Task success | 10%, pending | pending | pending | not scored in this run |
| Maintenance & community | 7% (8.8 this run) | 60 | 15 | OpenWeather One Call API +45 |
| Transparency & trust | 7% (8.8 this run) | 61 | 45 | OpenWeather One Call API +16 |
| Negative events | ≤15 | 0 | 0 | |
| **Total** | | **57.4 · C** | **39.9 · E** | |

## Facts side by side

| Fact | OpenWeather One Call API | Stormglass API |
| --- | --- | --- |
| Kind | HTTP API | HTTP API |
| Vendor | OpenWeather | Storm Glass AB |
| Hosted endpoint | `https://api.openweathermap.org/data/3.0/onecall` | `https://api.stormglass.io/v2` |
| Transports | HTTP, Streamable HTTP | HTTP |
| Auth | API key | API key |
| Pricing | Freemium | Freemium |
| x402 | no | no |
| Licence | none | Proprietary service under Storm Glass AB's Terms and Conditions. The Free and Small plans are not for commercial use |
| Tools exposed | 6 | none |
| Read-only variant documented | no | no |
| llms.txt | yes | no |
| MCP registry | `org.openweathermap/agents` | not listed |
| Last release | none | 2026-02-26 |
| Terms last updated |  | no date given |
| Privacy policy last updated | 2022-07-18 | no date given |
| Customer content may train models |  | not found in the text |
| Terms restrict automated access |  | not found in the text |
| Terms restrict benchmarking |  | not found in the text |
| Terms or service can change without notice |  | yes |
| Arbitration or class-action waiver |  | yes |
| 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.

**Stormglass API.** A read-only weather and marine API with about 70 hourly parameters, per-source values from named national models, tide data and ERA5 history from 2014. No OpenAPI file, status page, SDK or security page was found, the free plan allows 10 requests a day, and the docs and FAQ disagree on the status code for a spent quota.

## 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

### Stormglass API

1. Send the key as `Authorization: KEY` with no Bearer prefix. A missing or wrong key returns 403 with `{"errors":{"key":"API key is invalid"}}`
2. Always pass `source=sg` or a short source list on `/weather/point`. The default is every source, which multiplies the size of each hourly record
3. Treat 402 as a spent daily quota, not a billing failure, and stop until the next day. Read `meta.requestCount` against `meta.dailyQuota` on each response
4. Use `/historical/point` for past dates, at most 10 days a call and nothing newer than about 7 days. `/weather/point` looks back 14 days only
5. Send and read all times in UTC. Tide sea levels are relative to the chosen datum (MSL by default) and are not water depth

## Questions

### Which is better for AI agents, OpenWeather One Call API or Stormglass API?

OpenWeather One Call API scores 57.4 (C) on agent readiness against Stormglass API's 39.9 (E), and leads in 6 of 7 scored categories.

### Do OpenWeather One Call API and Stormglass API need an API key?

Both need an API key.

### Can an agent call OpenWeather One Call API and Stormglass API without installing anything?

Yes. OpenWeather One Call API has a hosted endpoint at https://api.openweathermap.org/data/3.0/onecall and Stormglass API at https://api.stormglass.io/v2.


## For agents

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

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