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nginx-certbot-mcp

by julcap
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check_cert_expiry

Read-only

List all Certbot-managed certificates with their expiry dates and days remaining to identify upcoming expirations across the entire server, including certs not tied to active nginx sites.

Instructions

List every certbot-managed certificate on the box with its expiry date and days remaining, via certbot certificates. Read-only. Covers all certs certbot knows about, not just domains with an active nginx site.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault

No arguments

Output Schema

TableJSON Schema
NameRequiredDescriptionDefault
certificatesYes

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed2 schema fields changedv0.1.2
    • addedOutput schema / properties / certificates / items / properties / domains
      Added value: +{
+  "description": "Every name on the certificate, e.g. example.com and *.example.com",
+  "items": {
+    "type": "string"
+  },
+  "type": "array"
+}
    • changedOutput schema / properties / certificates / items / required
      Previous value: -[
-  "domain",
-  "expires_at",
-  "days_remaining",
-  "auto_renew_enabled"
-]New value: +[
+  "domain",
+  "domains",
+  "expires_at",
+  "days_remaining",
+  "auto_renew_enabled"
+]
  2. Changed1 schema field changedv0.1.1
    • changedOutput schema / (root)
      Previous value: -nullNew value: +{
+  "$schema": "http://json-schema.org/draft-07/schema#",
+  "additionalProperties": false,
+  "properties": {
+    "certificates": {
+      "items": {
+        "additionalProperties": false,
+        "properties": {
+          "auto_renew_enabled": {
+            "type": "boolean"
+          },
+          "days_remaining": {
+            "description": "Negative if the certificate has already expired",
+            "maximum": 9007199254740991,
+            "minimum": -9007199254740991,
+            "type": "integer"
+          },
+          "domain": {
+            "type": "string"
+          },
+          "expires_at": {
+            "description": "Expiry date/time as reported by certbot",
+            "type": "string"
+          }
+        },
+        "required": [
+          "domain",
+          "expires_at",
+          "days_remaining",
+          "auto_renew_enabled"
+        ],
+        "type": "object"
+      },
+      "type": "array"
+    }
+  },
+  "required": [
+    "certificates"
+  ],
+  "type": "object"
+}
  3. First observedv0.1.0

TDQS

A4.5/5.0
Behavior4/5

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

Annotations already declare readOnlyHint=true and the description redundantly states 'Read-only.' However, the description adds the behavioral detail that it executes 'certbot certificates' and covers all certs, which goes beyond the annotation. It does not describe potential edge cases (e.g., no certs) but the output schema likely covers the return shape.

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?

Two sentences, no redundancy except the read-only note (which is harmless). The first sentence is action-oriented and front-loaded; the second adds necessary scope clarification. Every word earns its place.

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?

For a zero-parameter, read-only check tool, the description is complete: it states what it lists, how it does it, and its scope. The presence of an output schema means return value details are covered elsewhere. No additional information is needed for an agent to invoke it correctly.

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

Parameters4/5

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

The tool has zero parameters, so the description adds no parameter specifics—correctly so. With schema coverage at 100% (empty properties) and baseline for 0 params set at 4, the description needs no extra parameter info and appropriately remains silent on params.

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?

The description clearly states the verb 'List' with a specific resource (certbot-managed certificates on the box) and the output (expiry date and days remaining). It also distinguishes its scope from similar tools by clarifying it covers all certs, not just those with an active nginx site, which differentiates it from sibling tools like list_sites or renew_cert.

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

Usage Guidelines4/5

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

The description provides clear context that this tool is for checking certificate expiry and explicitly notes it covers all certs, not only those with active nginx sites. While it doesn't name alternative tools, the scope clarification helps an agent decide when to use it over other cert-related tools. A higher score would require explicit when/not-when guidance.

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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