nginx-certbot-mcp

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check_cert_expiry

Read-only

List every Certbot-managed certificate with its expiry date and days remaining, covering all certificates on the server, to monitor renewal needs.

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

Name	Required	Description	Default
No arguments

Output Schema

TableJSON Schema

Name	Required	Description	Default
`certificates`	Yes

Schema Changelog

Changes observed during successful MCP inspections.

Changed1 schema field changedv0.1.1Sep 15, 2026

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"
+}

First observedv0.1.0Sep 15, 2026

TDQS

A4.3/5.0

Behavior4/5

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

Annotations already carry readOnlyHint=true and openWorldHint=false, and the description's 'Read-only' merely reinforces that rather than contradicting it. Beyond the annotation, it adds meaningful behavior: execution via `certbot certificates` and the coverage scope of all certs certbot knows about, including domains without an active nginx site. No annotation contradiction.

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 short sentences with the core purpose front-loaded, followed by the mechanism and a scope qualifier. Every sentence earns its place, and the caveat about inactive nginx domains prevents a realistic mis-assumption.

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 tool that has an output schema and a readOnlyHint annotation, the description is complete: it states what is listed, the mechanism, and the precise coverage boundary. Nothing an agent needs to call it correctly is missing.

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 takes zero parameters, so the empty schema needs no elaboration and the 0-param baseline of 4 applies. The description adds no parameter details, and none are required.

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 states a specific verb ('List'), resource ('certbot-managed certificates'), and the exact data returned (expiry date, days remaining), plus the underlying command. The read-only listing framing clearly distinguishes it from the cert-management siblings (issue_cert, renew_cert, revoke_cert, delete_cert) without needing to open a schema.

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

Usage Guidelines3/5

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

The 'List every certbot-managed certificate' phrasing plus 'Read-only' implies this is the inspection tool within the cert family, and the scope note ('not just domains with an active nginx site') sets a useful expectation. However, it never names a specific alternative or states an explicit when-to-use/when-not-to-use rule — sibling differentiation is left to inference.

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