# Stormglass API vs Tomorrow.io Weather API

> Tomorrow.io Weather scores 51.4 (D) 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/stormglass-vs-tomorrow-io
- Markdown: https://www.anchorterminal.com/compare/stormglass-vs-tomorrow-io.md (~2,900 tokens)
- Slim: https://www.anchorterminal.com/compare/stormglass-vs-tomorrow-io.min.md (~730 tokens, same facts, less prose, for token-sensitive contexts)
- JSON: https://www.anchorterminal.com/compare/stormglass-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: 2026-10-09

Tomorrow.io Weather API scores 51.4 (D) on agent readiness against Stormglass API's 39.9 (E), and leads in 5 of 7 scored categories. Stormglass API leads on security & auth and payments & pricing. Both do weather forecasts.

- 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
- Tomorrow.io Weather API: grade D, 51.4/100, rank #751 of 950. Markdown https://www.anchorterminal.com/tools/tomorrow-io.md · JSON https://www.anchorterminal.com/api/v1/tools/tomorrow-io.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

### 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.

Ahead on:
- Security & auth, 44 against 34
- Payments & pricing, 25 against 20

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

### 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 34
- Schema & documentation, 75 against 40
- Agent ergonomics, 73 against 65
- Maintenance & community, 27 against 15
- Transparency & trust, 63 against 45

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


## Score by category

| Category | Weight | Stormglass API | Tomorrow.io Weather API | Edge |
| --- | --- | --- | --- | --- |
| Reliability | 16% (20 this run) | 34 | 55 | Tomorrow.io Weather API +21 |
| Performance | 10%, pending | pending | pending | not scored in this run |
| Schema & documentation | 13% (16.2 this run) | 40 | 75 | Tomorrow.io Weather API +35 |
| Agent ergonomics | 13% (16.2 this run) | 65 | 73 | Tomorrow.io Weather API +8 |
| Security & auth | 14% (17.5 this run) | 44 | 34 | Stormglass API +10 |
| Payments & pricing | 10% (12.5 this run) | 25 | 20 | Stormglass API +5 |
| Task success | 10%, pending | pending | pending | not scored in this run |
| Maintenance & community | 7% (8.8 this run) | 15 | 27 | Tomorrow.io Weather API +12 |
| Transparency & trust | 7% (8.8 this run) | 45 | 63 | Tomorrow.io Weather API +18 |
| Negative events | ≤15 | 0 | 0 | |
| **Total** | | **39.9 · E** | **51.4 · D** | |

## Facts side by side

| Fact | Stormglass API | Tomorrow.io Weather API |
| --- | --- | --- |
| Kind | HTTP API | HTTP API |
| Vendor | Storm Glass AB | The Tomorrow Companies Inc. |
| Hosted endpoint | `https://api.stormglass.io/v2` | `https://api.tomorrow.io/v4` |
| Transports | HTTP | HTTP |
| Auth | API key | OAuth or key |
| Pricing | Freemium | Freemium |
| x402 | no | no |
| Licence | Proprietary service under Storm Glass AB's Terms and Conditions. The Free and Small plans are not for commercial use | Proprietary service under Tomorrow.io's subscription terms |
| Tools exposed | none | 11 |
| Read-only variant documented | no | no |
| llms.txt | no | yes |
| Last release | 2026-02-26 | 2026-07-14 |
| Terms last updated | no date given | couldn't be read |
| Privacy policy last updated | no date given | couldn't be read |
| Customer content may train models | not found in the text | couldn't be read |
| Terms restrict automated access | not found in the text | couldn't be read |
| Terms restrict benchmarking | not found in the text | couldn't be read |
| Terms or service can change without notice | yes | couldn't be read |
| Arbitration or class-action waiver | yes | couldn't be read |

## Verdicts

**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.

**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

### 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

### 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, Stormglass API or Tomorrow.io Weather API?

Tomorrow.io Weather API scores 51.4 (D) on agent readiness against Stormglass API's 39.9 (E), and leads in 5 of 7 scored categories. Stormglass API leads on security & auth and payments & pricing.

### Do Stormglass API and Tomorrow.io Weather API need an API key?

Stormglass API needs an API key. Tomorrow.io Weather API takes an API key or an OAuth sign-in.

### Can an agent call Stormglass API and Tomorrow.io Weather API without installing anything?

Yes. Stormglass API has a hosted endpoint at https://api.stormglass.io/v2 and Tomorrow.io Weather API at https://api.tomorrow.io/v4.


## For agents

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

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- [AccuWeather Core Weather API + MCP vs Tomorrow.io Weather API](https://www.anchorterminal.com/compare/accuweather-api-vs-tomorrow-io.md)
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- [meteoblue Weather API vs Stormglass API](https://www.anchorterminal.com/compare/meteoblue-vs-stormglass.md)
- [Meteomatics Weather API vs Stormglass API](https://www.anchorterminal.com/compare/meteomatics-vs-stormglass.md)
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- [OpenWeather One Call API vs Stormglass API](https://www.anchorterminal.com/compare/openweather-one-call-vs-stormglass.md)
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