SDG Connection Test

A small, auditable diagnostic for proving or disproving whether a specific ISP is blocking or throttling the UDP traffic that Space Engineers, Torch, and Steam depend on.

SHA256 checksums for both files are published on the latest release page.

How to run it

Easy-install (Windows, recommended for most)

1. Click Download for Windows above.
2. Right-click the downloaded zip and choose Extract All.
3. Open the extracted folder. Read README - START HERE.txt if you'd like the same instructions in writing, then double-click Run-Test.cmd.
4. A black console window opens. Wait about 3-4 minutes — most of that is two 30+60 second “NAT idle” checks that have to wait the full interval to see whether your carrier's connection survives. Do not close the window; it closes itself when finished.
5. When it finishes, a file named sdg-test-report-<timestamp>.json appears in the same folder as Run-Test.cmd. Attach that file to your SDG support ticket.

If Windows shows a “protected your PC” warning, click More info then Run anyway. The bundle is unsigned; the SHA256 checksum on the release page lets you verify it before running. Your public IP address is redacted in the report and on screen by default; pass --include-public-ip only if SDG support specifically asks for it (this requires running from a terminal — see the developer path below).

Source / developer (Linux, macOS, or hands-on Windows)

1. Install Node.js 20 or later (LTS is fine).
2. Click Download source zip above and unzip it, or git clone the repository.
3. Open a terminal (PowerShell, cmd, or bash) in the unzipped folder.
4. Run:

   node client/client.js --host 38.107.232.39

   That IP is SDG's public connection-test server. If SDG support has given you a different endpoint, substitute it in place of 38.107.232.39.
5. Review the “what this will do” summary, press y, and wait. The default run takes about 3-4 minutes.
6. If SDG asked for a JSON report, re-run with --json report.json and send the file back. Your public IP is redacted in both the console output and the report by default; pass --include-public-ip only if SDG support specifically asks for it.

What it does

The client probes every TCP and UDP port that Space Engineers, Torch, and Steam actually use, then runs a battery of diagnostics targeting the specific ways internet providers (especially cellular and 5G home internet) commonly break online gaming. Results print to the console and, on request, to a JSON file.

The included tests, in plain English:

• Reachability, loss, and latency on every game and Steam port. Catches obvious blocks.
• Adaptive MTU discovery — walks UDP packet sizes downward from 1472 bytes to find the actual largest size your network can carry, then spot-checks that size on every UDP port. On 5G home internet across all major US providers, the carrier's mobile sub-tunnel commonly clamps UDP MTU somewhere in the 1280-1400 range; the tool names the exact ceiling.
• Real Steam server query on UDP 27015 — the exact same query the Steam server browser makes.
• Game-shape sustained test — 10 seconds of traffic at the same packet rate and size distribution real Space Engineers uses, in both directions.
• NAT timeout check — finds out whether your carrier closes idle connections after 30 or 60 seconds. This is the most common cause of “I get disconnected from the server every few minutes” on 5G home internet across all major US providers.
• NAT type — classifies your network as “cone” (peer-to-peer works) or “symmetric” (peer-to-peer needs a relay).
• Burst-vs-steady — sends a quick burst of packets and a slow steady stream and compares the loss patterns. Distinguishes ISP throttling from random network loss.
• Source-port and payload-shape variation — detects whether your ISP is treating different connections or different kinds of game traffic differently.
• Recommendation engine — turns the raw findings into plain-English next steps. When MTU is clamped, it gives you the exact copy-paste netsh command to fix it on Windows. Always renders a RECOMMENDATIONS section at the bottom of the console output, even on clean runs.
• Test-inconclusive banner — if more than half the UDP probes failed, a critical banner prints above the per-port table so you don't mistake an unreachable test server for a clean run.

It does not read your files, environment variables, browsing history, Steam install, or anything else off your machine. It only sends the test packets to the host you pass on the command line. The recommendation engine runs entirely locally — the suggested fix commands are plain text written to the report file; the tool never executes them itself.

Why you can trust it

The client is a single ~3,000-line JavaScript file with zero runtime dependencies. The whole thing — client plus three small shared helpers — is about 3,500 lines of commented JavaScript and is written to be skimmable in about thirty minutes. Three layers of audit:

• Read the source — client/client.js on GitHub. The transparency notes walk through what to grep for and what each match means.
• Watch the packets — run with Wireshark capturing on your active NIC. Every outbound packet has the same 8-byte session nonce printed at startup, so you can filter by it. Every packet matches one of the layouts in the protocol spec.
• Run it in a sandbox — Windows Sandbox, a throwaway VM, or a Docker node:20-alpine container all work.

What the server logs

The operator-deployed server records minimal session metadata for diagnostic correlation: source IP, source ASN/ISP, a client-generated nonce (printed at client startup so you can correlate captures), per-port packet counts, and rate-limit counters. Logs are capped at ~100 MB total on disk, never shipped off-host, and never correlated with Steam or in-game identity. Full detail in the privacy notice.

Source & license

MIT-licensed. The client and shared protocol code live at github.com/sdg-net/sdg-connection-test. The server implementation is operator-internal; the security model and behavioral guarantees are spelled out in SECURITY.md.

Built by SDG. Hosted at sdg.knowledgeondemand.net. Source: github.com/sdg-net/sdg-connection-test.