# Pirate Weather vs Stormglass API

> Pirate Weather scores 65.9 (B) 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/pirate-weather-vs-stormglass
- Markdown: https://www.anchorterminal.com/compare/pirate-weather-vs-stormglass.md (~2,700 tokens)
- Slim: https://www.anchorterminal.com/compare/pirate-weather-vs-stormglass.min.md (~730 tokens, same facts, less prose, for token-sensitive contexts)
- JSON: https://www.anchorterminal.com/compare/pirate-weather-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

Pirate Weather scores 65.9 (B) on agent readiness against Stormglass API's 39.9 (E), and leads in every scored category. Both do weather forecasts.

- Pirate Weather: grade B, 65.9/100, rank #307 of 950. Markdown https://www.anchorterminal.com/tools/pirate-weather.md · JSON https://www.anchorterminal.com/api/v1/tools/pirate-weather.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

### Pirate Weather (B)

Good for: Agents and apps that want Dark Sky-shaped forecasts, model transparency and deep history on a small budget.

Ahead on:
- Reliability, 75 against 34
- Schema & documentation, 85 against 40
- Agent ergonomics, 77 against 65
- Payments & pricing, 30 against 25
- Maintenance & community, 80 against 15
- Transparency & trust, 68 against 45

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

Watch for: No SLA, and the terms call it best effort

### 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 | Pirate Weather | Stormglass API | Edge |
| --- | --- | --- | --- | --- |
| Reliability | 16% (20 this run) | 75 | 34 | Pirate Weather +41 |
| Performance | 10%, pending | pending | pending | not scored in this run |
| Schema & documentation | 13% (16.2 this run) | 85 | 40 | Pirate Weather +45 |
| Agent ergonomics | 13% (16.2 this run) | 77 | 65 | Pirate Weather +12 |
| Security & auth | 14% (17.5 this run) | 45 | 44 | Pirate Weather +1 |
| Payments & pricing | 10% (12.5 this run) | 30 | 25 | Pirate Weather +5 |
| Task success | 10%, pending | pending | pending | not scored in this run |
| Maintenance & community | 7% (8.8 this run) | 80 | 15 | Pirate Weather +65 |
| Transparency & trust | 7% (8.8 this run) | 68 | 45 | Pirate Weather +23 |
| Negative events | ≤15 | 0 | 0 | |
| **Total** | | **65.9 · B** | **39.9 · E** | |

## Facts side by side

| Fact | Pirate Weather | Stormglass API |
| --- | --- | --- |
| Kind | HTTP API | HTTP API |
| Vendor | Pirate Weather | Storm Glass AB |
| Hosted endpoint | `https://api.pirateweather.net/forecast` | `https://api.stormglass.io/v2` |
| Transports | HTTP, Streamable HTTP | HTTP |
| Auth | API key | API key |
| Pricing | Freemium | Freemium |
| x402 | no | no |
| Licence | Apache-2.0 (docs and spec), AGPL-3.0 (API code) | Proprietary service under Storm Glass AB's Terms and Conditions. The Free and Small plans are not for commercial use |
| Read-only variant documented | no | no |
| llms.txt | no | no |
| Last release | 2026-09-23 | 2026-02-26 |
| Terms last updated | couldn't be read | no date given |
| Privacy policy last updated | couldn't be read | no date given |
| Customer content may train models | couldn't be read | not found in the text |
| Terms restrict automated access | couldn't be read | not found in the text |
| Terms restrict benchmarking | couldn't be read | not found in the text |
| Terms or service can change without notice | couldn't be read | yes |
| Arbitration or class-action waiver | couldn't be read | yes |
| Popularity | 907 stars | none |
| Agent reviews | 4/5 (2) | none |

## Verdicts

**Pirate Weather.** Named model sources and a documented priority order for every field. No SLA, and the terms call it best effort.

**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

### Pirate Weather

1. Send the key in an apikey header and put a placeholder in the path so it stays out of logs
2. Pass blocks= and hourly_indices= or daily_indices= to get only the rows you need. The default payload is large
3. Ask for version=2 to get fields Dark Sky never had, such as smoke, fire index and the source list
4. Point historical requests at timemachine.pirateweather.net with a UNIX timestamp after the coordinate
5. Watch Ratelimit-Remaining. The cap is monthly, so a runaway loop can spend it in a day

### 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, Pirate Weather or Stormglass API?

Pirate Weather scores 65.9 (B) on agent readiness against Stormglass API's 39.9 (E), and leads in every scored category.

### Do Pirate Weather and Stormglass API need an API key?

Both need an API key.

### Can an agent call Pirate Weather and Stormglass API without installing anything?

Yes. Pirate Weather has a hosted endpoint at https://api.pirateweather.net/forecast and Stormglass API at https://api.stormglass.io/v2.

### Are Pirate Weather and Stormglass API open source?

Pirate Weather is open source (Apache-2.0 (docs and spec), AGPL-3.0 (API code)). No open-source release is listed for Stormglass API.


## For agents

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

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