{"uid":"cap_x55BnCYTYld2fYac2U2du","slug":"sitecheck-web-intel-http-3-alt-svc-advertiser-detector-f4c5b3a8","name":"SiteCheck Web Intel – HTTP/3 & Alt-Svc Advertiser Detector","description":"Reports which newer HTTP protocols a site advertises: HTTP/3 (h3) and older draft or HTTP/2 alternatives in its Alt-Svc response header, and the Alt-Svc max-age. This is what the server announces, not a TLS ALPN negotiation: the fetch this tool makes cannot choose the protocol, so a site that negotiates but does not send Alt-Svc will show as not advertised.","url":"https://api.webintel-api.workers.dev/api/security/tls-alpn-detector?utm_source=zero.xyz","method":"GET","headers":{},"bodySchema":{"type":"object","$schema":"https://json-schema.org/draft/2020-12/schema","required":["input"],"properties":{"input":{"type":"object","required":["type","method"],"properties":{"type":{"type":"string","const":"http"},"method":{"enum":["GET"],"type":"string"},"queryParams":{"type":"object","required":["domain"],"properties":{"domain":{"type":"string","description":"Domain name such as example.com (required)"}}}},"additionalProperties":false},"output":{"type":"object","required":["type"],"properties":{"type":{"type":"string"},"example":{"type":"object"}}}}},"responseSchema":{"type":"json","example":{"altSvc":"h3=\":443\"; ma=86400","domain":"cloudflare.com","source":"https://cloudflare.com/","finalUrl":"https://www.cloudflare.com/","checkedAt":"2026-10-24T02:12:26.033Z","advertised":["h3"],"httpStatus":200,"http3Advertised":true,"altSvcMaxAgeSeconds":86400}},"example":null,"exampleRequest":null,"tags":["x402"],"displayCostAmount":"0.002","displayCostAsset":"USDC","priceDynamic":false,"priceHint":null,"priceStatus":"priced","priceSource":"probe","requiresHandshake":false,"reviewCount":0,"rating":{"score":"0.00","successRate":"0.00","reviews":0,"stars":null,"state":"unrated"},"availabilityStatus":"unknown","priceObserved":null,"sessionDeposit":null,"pricing":{"kind":"static","summary":"$0.002/call","primary":{"kind":"static","protocol":"x402","network":"base","amountUsd":"0.002","per":"call","confidence":"exact"},"accepted":[{"kind":"static","protocol":"x402","network":"base","amountUsd":"0.002","per":"call","confidence":"exact"}]},"paymentMethods":[{"uid":"pm_cCrJ9qJ7K5pNTtldcwqZ-","protocol":"x402","methodType":"crypto","chain":"base","mode":"charge","costAmount":"0.002","costPer":"request","priority":0,"asset":"0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913","unit":"request","depositMicros":null,"planRef":null}],"brandName":null,"brandSlug":null,"brandBaseUrl":null,"brandDocsUrl":null,"whatItDoes":"Checks a domain's Alt-Svc response header to determine which newer HTTP protocols (HTTP/3, draft versions) it advertises and reports the max-age of that advertisement","exampleAgentPrompt":"Can you check whether cloudflare.com advertises HTTP/3 or any newer HTTP protocols in its Alt-Svc response header?","exampleUseCases":[{"title":"Verify HTTP/3 rollout on own domain","prompt":"Has our site nginx-demo.example.com actually started advertising HTTP/3 in its Alt-Svc header yet? I want to confirm the rollout is live."},{"title":"Competitive protocol benchmark","prompt":"Check whether shopify.com advertises HTTP/3 via Alt-Svc — I'm comparing CDN and protocol configurations across major e-commerce platforms."},{"title":"Monitor Alt-Svc max-age for caching policy","prompt":"What's the Alt-Svc max-age that stripe.com is broadcasting? I want to know how long clients will cache that protocol advertisement."}],"resultDescription":"Returns a JSON object with the domain checked, the raw Alt-Svc header string, a list of advertised protocols (e.g. ['h3']), a boolean http3Advertised flag, the Alt-Svc max-age in seconds, the HTTP status code of the fetch, the final URL after any redirects, and the timestamp of the check.","failureModes":["Domain does not send an Alt-Svc header — advertised array will be empty and http3Advertised will be false","Domain is unreachable or returns a non-2xx status — httpStatus reflects the error code","Invalid or malformed domain input — API may return an error or empty result","Site negotiates HTTP/3 via TLS ALPN but does not send Alt-Svc — will show as not advertised (by design limitation)","Redirects to a different final URL — finalUrl field reflects the redirected destination"],"whenToPreferThis":"Use this endpoint when you need to quickly determine whether a specific domain is broadcasting HTTP/3 or other protocol upgrades via its Alt-Svc header, without needing to perform a full TLS ALPN handshake. It is ideal for auditing CDN configurations, validating protocol rollouts, benchmarking competitor infrastructure, or monitoring Alt-Svc advertisement policies at scale. Note that it cannot detect HTTP/3 support that is only advertised via TLS ALPN and not via Alt-Svc headers.","instructions":null,"reviewSummary":null,"reviewSummaryHighlights":null,"reviewSummaryConcerns":null,"reviewSummaryGeneratedAt":null,"activationCount":0,"lastUsedAt":null,"lastSuccessfullyRanAt":null,"lastHealthCheckAt":"2026-10-24T12:40:36.436Z","isFirstParty":false,"canonicalSlug":"sitecheck-web-intel-http-3-alt-svc-advertiser-detector-f4c5b3a8"}