# Sentinel TCP Port Reachability Checker

> Sentinel TCP Port Reachability Checker is a paid API for AI agents from sentinel.rootstuff.io, paid per call via x402, $0.01/call, status unknown (last checked 2026-09-15).

Checks whether a specific TCP port on a host is reachable and measures the connection latency

## Facts

- Endpoint: GET https://sentinel.rootstuff.io/x402/port
- Price: $0.01/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-15
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/sentinel-tcp-port-reachability-checker-36f7fa4e
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_9fWikzUYUTQ24pBKDWYzm

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

## How to call it through Zero

Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`):

```sh
zero fetch --capability sentinel-tcp-port-reachability-checker-36f7fa4e
```

Example prompt: Can you check if TCP port 5432 is reachable on db.mycompany.com and tell me how long the connection takes?

## When to prefer this

Use this endpoint when you need a quick, cheap TCP-level connectivity check against a specific host and port — ideal for verifying firewall rules, diagnosing service outages, or confirming a port is open before attempting a connection. Prefer this over full HTTP probing endpoints when you only need raw TCP reachability and latency, not HTTP response content or headers.

## Known failure modes

- Host not found or unresolvable DNS — returns error indicating hostname could not be resolved
- Connection timeout — port may be firewalled or host unresponsive, returned as timeout status
- Invalid port number outside 1-65535 range — returns validation error
- Host is a private/internal IP that is not publicly routable — probe may fail or return unreachable
- Rate limiting or payment failure — returns 402 or rate-limit error

## How this service works

TCP port reachability and connect latency

## Output

Returns whether the TCP port is reachable (open/closed/timeout) and the measured connect latency in milliseconds for the given host and port combination.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "host": {
   "type": "string",
   "description": "Hostname or public IP."
  },
  "port": {
   "type": "integer",
   "description": "1 to 65535."
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/sentinel-tcp-port-reachability-checker-36f7fa4e/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from sentinel.rootstuff.io](https://www.zero.xyz/host/sentinel.rootstuff.io/llms.txt)