netchecker

A fast, cross-platform internet reachability checker. It probes your local network infrastructure, DNS, and a set of domestic / global / filtered websites in parallel, reporting each as PASS / FAIL / INFO with timings — in about 1–2 seconds.

Built for one annoying question: "my internet is technically up, but which parts actually work — the ISP, DNS, the proxy, the filtered sites?" Especially useful behind a VPN/proxy, where the answer differs per route.

===============================================
   netchecker — Network Standpoint Test
   Running Mode:  DIRECT
   Local IP:      192.168.1.6
   DNS resolvers: 192.168.1.1
===============================================

[+] Infrastructure Standpoints:
  [PASS] Local Network Interface        - Active on en0 (192.168.1.6) — Wi-Fi SSID: home
  [PASS] Ping Default Gateway (192.168.1.1) - reachable — 2 ms
  [PASS] Ping Raw Global IP (1.1.1.1)   - Global IP routing up — 4 ms

[+] DNS Resolution:
  [PASS] www.google.com                 - Resolved to 142.251.153.119 — 21 ms

[*] Domestic Websites (DIRECT Route):
  [PASS] digikala.com                   - HTTP 301 — 119 ms

Install

The recommended way is cargo binstall, which downloads a prebuilt binary from the GitHub Releases — no compiling:

cargo binstall netchecker

Don't have it yet? cargo install cargo-binstall (or grab it from its releases page).

Other options:

# Homebrew (macOS / Linux)
brew install pourmand1376/tap/netchecker

# Cargo (compile from source)
cargo install netchecker

# Nix
nix run github:pourmand1376/netchecker

# Debian / Ubuntu — grab the .deb from the Releases page
sudo apt install ./netchecker_*.deb

Or build from source: git clone, then cargo build --release.

Usage

netchecker        # auto: uses the system proxy if one is set, otherwise direct
netchecker -d     # force direct — bypass proxies, test the raw ISP path
netchecker -p     # force proxy — route global/filtered sites via the system proxy

With no arguments it picks the mode automatically; there is no prompt, so it's safe in scripts and cron. Domestic sites always use the direct route.

How it works

• DNS that can't wedge. A bad or just-changed macOS resolver makes getaddrinfo() (via mDNSResponder) serialise lookups and stall every "parallel" probe. netchecker resolves names itself with hickory-resolver, straight to the configured nameservers over UDP/53 — the OS resolver is never in the path, so a bad lookup fails fast instead of hanging everything.
• IP-pinned probes. On the direct route each HTTP probe is handed its pre-resolved IP, so it never calls the OS resolver either. Redirects aren't followed on that route (a cross-host redirect would re-trigger a lookup); a 3xx still counts as reachable.
• Reachability without root. No ICMP. TCP connects race a few common ports; a ConnectionRefused proves the host answered, so it counts as reachable. Only a host that fails on every port is reported down.
• True egress detection. The active interface is whichever local address the kernel would actually use to reach the internet (found via a UDP connect that sends nothing), not a heuristic — correct even on split-tunnel VPNs.

Platform support

The core — DNS bypass, HTTP probes, interface/gateway detection, TCP reachability — is native Rust and identical on all three platforms:

1. scutil --proxy (catches GUI-configured proxies) plus env vars.
2. HTTPS_PROXY / ALL_PROXY / HTTP_PROXY env vars.
3. Best-effort via ipconfig / networksetup; on macOS 14+ the SSID needs Location Services permission and may come back empty.
4. Best-effort via nmcli / iwgetid.
5. Best-effort via netsh wlan show interfaces.

SSID is the one genuinely fragile piece — there's no dependable cross-platform API. When it can't be read, netchecker shows "SSID unavailable or wired" rather than failing.

Customising the site list

The domestic / global / filtered lists live in src/sites.rs — edit and rebuild.

License

MIT — see LICENSE.