RunStack Checks

Port reachability from the internet

check_port

Read-onlyIdempotent

Check from the internet whether TCP ports of a public host are open, closed or filtered. Use to verify firewall / security group rules, or to find out why a service works locally but is unreachable from outside. Only public addresses are accepted; this does not test the application behind the port (use check_http or check_tls for that).

Input Schema

Name	Required	Description	Default
`host`	Yes	Public hostname or IP address, e.g. example.com or 203.0.113.10
`ports`	Yes	Comma-separated TCP ports, e.g. 22,80,443

Output Schema

Name	Required	Description
`ok`	Yes	false when the check could not run (see error / message)
`tool`	No
`error`	No	Error code when ok is false
`facts`	No
`notice`	No	Usage note, e.g. anonymous-tier limits
`target`	No	What was checked
`message`	No
`verdict`	No
`findings`	No
`headline`	No	One-line summary
`reportUrl`	No	Shareable report link

Schema Changelog

Changes observed during successful MCP inspections.

Changed1 schema field changedOct 18, 2026

addedOutput schema / properties / notice

Added value: +{
+  "description": "Usage note, e.g. anonymous-tier limits",
+  "type": "string"
+}

Changed4 schema fields changedOct 18, 2026

addedInput schema / additionalProperties
```
Added value: +false
```

changedInput schema / properties / host / description

Previous value: -"Public hostname or IP"New value: +"Public hostname or IP address, e.g. example.com or 203.0.113.10"

changedInput schema / properties / ports / description

Previous value: -"Comma-separated ports, e.g. 22,443"New value: +"Comma-separated TCP ports, e.g. 22,80,443"

changedOutput schema / (root)

Previous value: -nullNew value: +{
+  "properties": {
+    "error": {
+      "description": "Error code when ok is false",
+      "type": "string"
+    },
+    "facts": {
+      "items": {
+        "properties": {
+          "label": {
+            "type": "string"
+          },
+          "value": {
+            "type": "string"
+          }
+        },
+        "required": [
+          "label",
+          "value"
+        ],
+        "type": "object"
+      },
+      "type": "array"
+    },
+    "findings": {
+      "items": {
+        "properties": {
+          "code": {
+            "type": "string"
+          },
+          "detail": {
+            "description": "Why it matters / cause",
+            "type": "string"
+          },
+          "docs": {
+            "description": "How-to article URL",
+            "type": "string"
+          },
+          "fix": {
+            "description": "How to fix",
+            "type": "string"
+          },
+          "severity": {
+            "enum": [
+              "error",
+              "warning",
+              "info",
+              "ok"
+            ],
+            "type": "string"
+          },
+          "title": {
+            "type": "string"
+          }
+        },
+        "required": [
+          "severity",
+          "title"
+        ],
+        "type": "object"
+      },
+      "type": "array"
+    },
+    "headline": {
+      "description": "One-line summary",
+      "type": "string"
+    },
+    "message": {
+      "type": "string"
+    },
+    "ok": {
+      "description": "false when the check could not run (see error / message)",
+      "type": "boolean"
+    },
+    "reportUrl": {
+      "description": "Shareable report link",
+      "type": "string"
+    },
+    "target": {
+      "description": "What was checked",
+      "type": "string"
+    },
+    "tool": {
+      "type": "string"
+    },
+    "verdict": {
+      "enum": [
+        "ok",
+        "warn",
+        "fail"
+      ],
+      "type": "string"
+    }
+  },
+  "required": [
+    "ok"
+  ],
+  "type": "object"
+}

First observedOct 17, 2026

TDQS

A4.5/5.0

Behavior4/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare readOnly, idempotent, openWorld and non-destructive, so the safety profile is covered. The description adds genuinely new context: the check originates from the internet (external vantage point) and only public addresses are accepted, a real constraint not expressed in the schema. It stops short of noting rate limits or timeout behavior.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Three sentences, each earning its place: capability, use cases, and constraints/alternatives. The core capability is front-loaded with zero filler.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

With an output schema present and annotations covering safety, the description supplies everything else an agent needs — scope, vantage point, address restrictions, and sibling routing. Nothing material is missing.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100% and both parameters are documented with examples in the schema itself, so the description adds no syntax or format detail beyond it. Baseline 3 applies.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb and resource ('Check from the internet whether TCP ports of a public host are open, closed or filtered') and immediately names the outcome taxonomy. An agent can distinguish this from check_ip or check_dns without opening the schema.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines5/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Gives explicit use cases (verify firewall/security group rules, diagnose local-vs-external reachability) and explicit exclusions, directing application-layer checks to check_http or check_tls. Both when-to-use and when-not-to-use are covered.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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