7Timer!

Implementation notes

When to use 7Timer!

7Timer! is a rare survivor from the pre-monetization era of public APIs — running since 2006, backed by NOAA GFS numerical weather model data, completely key-free, and truly unlimited. It exists because Chinese astronomers built it for observing conditions (cloud cover, atmospheric seeing) and the tool escaped academic use. Choose 7Timer! for weekend projects, hobby dashboards, embedded systems where you can't manage API keys, and astronomy applications where you need the specific 'astro' output (seeing, transparency, moon phase). Do not choose it for anything customer-facing production — the API design is dated, docs are sparse, and there's no SLA.

Common pitfalls

• Default response format is XML, not JSON. Pass `&output=json` on every call or you'll spend time debugging an XML parser you didn't plan to add.
• The forecast resolution is 3-hour intervals, not hourly — high enough for most use cases but insufficient for minute-level rain prediction.
• Variable names are short and undocumented (`cloudcover`, `prec_type`, `rh2m`, `seeing`). The maintainer's documentation page is sparse; expect to inspect a sample response to figure out what each field means.

Quick start (bash)

curl "https://www.7timer.info/bin/api.pl?lon=2.35&lat=48.85&product=civil&output=json"

From our monitoring

7Timer! has been remarkably durable in our monitoring — 99%+ uptime with response times around 500-800ms globally (the servers are in China, so latency from the Americas is higher than commercial APIs hosted on CDN). The service has NEVER introduced monetization or paywalls in its 20-year history, which is genuinely unusual. Trust it for what it is: a free amateur-astronomer resource that stayed free. The forecast quality is on par with any GFS-based provider (which is to say: adequate for general use, less good than ECMWF-based providers like Open-Meteo or MET Norway for European weather).

Production integration patterns

Astronomy observation planning

7Timer's `astro` product (as opposed to `civil` or `civillight`) returns fields specifically useful for optical astronomy: `seeing` (atmospheric stability, 1-5 scale), `transparency` (sky clarity, 1-8 scale), and cloud cover in a form that maps to observability. Amateur astronomy apps use these fields directly to compute a 'good night for observation' score. No other free weather API returns this data — you'd be using Meteoblue's paid tier or computing it yourself from raw temperature/humidity/pressure otherwise.

Fallback tier in a weather stack

For weather apps that already use Open-Meteo or MET Norway as primary, 7Timer is a natural fallback tier when the primary fails. It's completely no-key, so no auth setup needed. It's unlimited, so no rate-limit concerns during outages. The 3-hour resolution isn't as good as hourly, but degraded service beats no service. Wire it up as a fallback in your adapter layer — one afternoon of work, saves users during your primary's next outage.

Compared to the closest paid alternatives

vs Open-Meteo — Both free with generous limits; Open-Meteo commercial at €29/mo

Open-Meteo has hourly resolution (7Timer has 3-hour), a much better documented API, sub-300ms response times, and a modern JSON structure. For any general weather use case, Open-Meteo wins on every measurable dimension. 7Timer's advantages are the astro-specific data and the 'no key ever' policy for embedded systems or minimal-config projects.

vs Meteoblue (paid) — No free tier · Basic: ~$50/month

Meteoblue is the professional-astronomy weather service — extensive seeing forecasts, cloud model comparisons, observatory-specific outputs. Paid-only starting around $50/month. For hobby astronomers 7Timer is enough; for observatory operations Meteoblue is the industry standard.

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