Captive portal endpoint atlas

WiFi 4 Breakfast

A fixed plain-HTTP contract for portal discovery.

The local rescue service returns a fixed page at `/` and the exact body `W4B_HTTP_OK_V1` at `/probe/v1/http` when our server is reached. It accepts no query data, sets no cookie, performs no redirect, and sends no HSTS header.

Production host placement remains open until the candidate domain and topology are field-tested.

Platform reference

Expected responses vary by platform and version.

Firefox documents a regular request to `http://detectportal.firefox.com/canonical.html`. Microsoft documents HTTP active probes to its configured NCSI host and an expected `Microsoft Connect Test` payload. Chromium changed its captive detection origin to `http://connectivitycheck.gstatic.com/generate_204` in August 2025.

Apple documents automatic probing and standards-based captive network advertisement, but the current first-party guidance used here does not define a stable public probe URL. The atlas therefore does not invent one.

• Firefox: `http://detectportal.firefox.com/canonical.html`, documented by Mozilla.
• Windows NCSI: configured Microsoft HTTP probe host and expected payload, documented by Microsoft.
• Chromium: `http://connectivitycheck.gstatic.com/generate_204`, documented in Chromium source.
• Apple: automatic probe behavior and CAPPORT support, exact public probe URL intentionally omitted.

Use this data

Recheck before relying on any endpoint.

Endpoint behavior can change without becoming an application API. Do not hard-code third-party endpoints into W4B product logic without a current source, direct test, privacy review, failure fallback, and maintenance owner.

Downloads

Use the source material.

Sources

First-party references.

1. Captive portal detectionMozilla Support
2. Network Connectivity Status Indicator overviewMicrosoft Learn
3. Chromium captive portal detection endpoint changeChromium source
4. How to modernize your captive networkApple Developer
5. RFC 8952: Captive Portal ArchitectureInternet Engineering Task Force

Keep going

Related help.