Free tool

China Firewall Test

Test whether a URL is reachable from inside mainland China — and which of its third-party dependencies are not.

By the 21YunBox China Engineering Team · Reviewed 2026-08-27 · Probes located in mainland China

Short answer A site is reachable in China when a request from inside the mainland completes. Most enterprise sites are not blocked outright — they stall on individual third-party hosts that never answer. Reachability is not the same as permission to operate: anything actually served from inside mainland China also needs an ICP filing, which is triggered by where the server sits, not by where the company is.

Not loading? Open the China Firewall Test directly.

The test is executed by 21YunBox probe servers inside mainland China. Requests to sites hosted outside China are slower by design — that delay is part of the result.

What the result actually tells you

A pass/fail on the page URL is the least useful part of the answer. There are three different delivery paths a site can take into China, and this test only distinguishes the first two:

Delivery path	Where the request ends	ICP filing required	What this test shows
Offshore origin (most sites today)	Outside China. Every request crosses a congested, filtered border.	No	Reachable or not, plus which dependencies fail
Nearshore edge (Hong Kong / Singapore nodes)	Still outside the mainland. The crossing is shorter, not removed.	No — because it never enters China	Usually reachable, still crossing the border
In-China delivery	Inside the mainland. No border crossing on the request path.	Yes	Not measurable from this test alone

The third row is the one worth understanding before you choose. Removing the round trip means serving from inside mainland China, and serving from inside mainland China is exactly the thing that triggers the filing requirement. A nearshore node moves the endpoint of the crossing closer; it does not remove the crossing. So the arrangement that avoids the filing is also the arrangement that keeps the latency — the two are the same decision, not two separate ones.

Three properties of ICP filing catch most teams late: it is triggered by server location, it requires a mainland legal entity, and it is bound to the access provider — not only to the domain. Change hosting provider without updating the filing and the record goes stale. The Ministry of Industry and Information Technology publishes the record itself at beian.miit.gov.cn.

What we measured with this, from inside China

We ran the same reference page through four delivery arrangements and measured each from a probe in Shanghai, five interleaved rounds, on 2026-08-28. The result is not a latency ranking — it is a completion result.

Delivery arrangement	Time to first byte	Finished loading within 60s	Embedded video & form verification
Offshore origin	140ms	0 / 5	0 / 5
Nearshore edge (Hong Kong)	35ms	0 / 5	0 / 5
Inside mainland China, ICP filed	33ms	0 / 5	0 / 5
Inside mainland China, via the 21YunBox Optimizer	493ms	5 / 5	5 / 5

Note the third row. It is served from inside mainland China under a live ICP filing, it posted the best time to first byte of all four, and it failed exactly as completely as serving the page from the other side of the Pacific — the video never played and the form could never be submitted, on every attempt. The fastest first byte belonged to a path that never finished loading.

Probe on a different network from every measurement target, so no path had a home-network advantage. First-party assets byte-identical across the first three arrangements, verified by checksum before each run. The probe is a datacenter line, which has better international transit than a corporate connection — these figures are a floor, not a worst case. Full method and limits →

Frequently Asked Questions

How do I test if my website is blocked in China?

Enter your URL in the test above. The request is made by probe servers located inside mainland China, so the result reflects what a visitor in China actually gets — not what a test run from outside the country reports. A test from outside China cannot tell you this, because the filtering happens at the border.

My site loads, but the test still shows failures. Why?

Most enterprise sites are not blocked as a whole. Individual third-party requests are — fonts, analytics, tag managers, authentication SDKs, video players and map APIs hosted on unreachable domains. The page shell arrives and then stalls waiting for resources that will never answer. This is the most common failure pattern we see, and it is why a page can be "up" in China and still be unusable.

Can a CDN fix a blocked resource?

No. A CDN makes a reachable host closer. It cannot make an unreachable host answer. If your page requests a domain that is filtered at the border, caching that request somewhere else does not change the outcome — the browser still asks for the original host. Blocked dependencies have to be replaced or routed through a same-origin path that is served from inside China — which is what the 21YunBox Optimizer does. They cannot be accelerated.

Does passing this test mean my site is allowed to operate in China?

No — and these are two separate questions that are often confused. Reachability is technical. Permission to operate is regulatory: any site actually served from inside mainland China needs an ICP filing, which requires a mainland legal entity and is bound to the access provider, not just the domain. A site can pass this test and still have no legal basis to be served from inside China.

Is the test free?

Yes. No account and no email address are required to run it.