网站可用性检查器
从多个来源检查网站是否正常运行。此工具使用独立 API 和直接连接尝试测试网站可用性，即使一个来源失败也能给出可靠答案。
什么是网站可用性？
网站可用性 refers to whether a website is accessible and responding to requests from the internet. A website can be "up" (available) or "down" (unavailable) due to various factors like server issues, network problems, DNS failures, or maintenance.
这个工具如何工作？
此工具使用多种检测方法，具有自动故障转移：
- isitup.org — Primary source, checks HTTP status from external servers
- down.com — Fallback source with independent verification
- 直接获取 — Attempts direct connection from your browser
- Cloudflare DNS — Verifies domain name resolution
如果一个来源失败，工具会自动尝试下一个。CORS 代理确保跨域请求从您的浏览器正常工作。
常见 HTTP 状态码
| 代码 | 含义 | 状态 |
|---|---|---|
| 200 | OK — Request successful | ✅ Online |
| 301/302 | Redirect — Moved permanently/temporarily | ✅ Online |
| 403 | Forbidden — Access denied | ⚠️ Restricted |
| 404 | Not Found — Page doesn't exist | ⚠️ Partial |
| 500 | 内部服务器错误 | ❌ Error |
| 502 | 错误网关 | ❌ Error |
| 503 | 服务不可用 | ❌ Down |
| 超时 | 服务器无响应 | ❌ Down |
网站为什么会宕机？
- 服务器过载 — Too many visitors or DDoS attacks
- 维护 — Scheduled updates or server migrations
- DNS 问题 — Domain name fails to resolve to an IP
- 网络问题 — ISP or routing issues
- SSL 证书过期 — HTTPS becomes invalid
- 托管服务商故障 — Data center issues
限制
- 速率限制 — Free APIs have usage limits; excessive checks may be temporarily blocked
- 地理差异 — A site may be accessible from one country but blocked in another
- CDN 缓存 — Results may reflect cached responses rather than real-time status
- 单时间点 — Status can change seconds after the check
- CORS 限制 — Direct browser checks are limited by cross-origin policies