domain-security-mcp-server

SSL/TLS Certificate Inspector

ssl_certificate

Read-onlyIdempotent

Inspect a domain's TLS certificate to reveal issuer, validity, expiry status, and trust warnings, flagging expired or soon-to-expire certs.

Instructions

Inspect the TLS certificate served by a host: issuer, subject, validity window, days-until-expiry, SANs, serial and SHA-256 fingerprint. Flags expired or soon-to-expire certificates.

Args:

domain (string): host to connect to.
port (number): TLS port (default 443).
response_format ('markdown' | 'json'): output format (default 'markdown').

Returns: certificate fields plus { days_until_expiry, expired, expires_soon, trusted, hostname_matches, authorization_error }. An untrusted certificate (self-signed, unknown root, wrong host) is still inspected and reported, never silently passed.

Example: "When does github.com's certificate expire?" -> ssl_certificate(domain="github.com"). Errors: returns an error if the host is unreachable or serves no certificate.

Input Schema

TableJSON Schema

Name	Required	Description	Default
`port`	No	TLS port (default 443).
`domain`	Yes	Domain (or host) to inspect, e.g. 'example.com'.
`response_format`	No	Output format: 'markdown' for a human-readable summary (default) or 'json' for the full structured payload.	markdown

Output Schema

TableJSON Schema

Name	Required	Description	Default
`host`	Yes
`port`	Yes
`expired`	Yes
`trusted`	Yes
`valid_to`	No
`valid_from`	No
`expires_soon`	Yes
`serial_number`	No
`hostname_matches`	Yes
`days_until_expiry`	No
`subject_alt_names`	Yes
`fingerprint_sha256`	No
`issuer_common_name`	No
`authorization_error`	No
`issuer_organization`	No
`subject_common_name`	No

Schema Changelog

Changes observed during successful MCP inspections.

Changed8 schema fields changedv1.2.1Sep 14, 2026

changedInput schema / $schema

Previous value: -"http://json-schema.org/draft-07/schema#"New value: +"https://json-schema.org/draft/2020-12/schema"

removedInput schema / additionalProperties
```
Removed value: -false
```
addedInput schema / properties / domain / maxLength
```
Added value: +253
```

changedOutput schema / $schema

Previous value: -"http://json-schema.org/draft-07/schema#"New value: +"https://json-schema.org/draft/2020-12/schema"

addedOutput schema / properties / authorization_error
```
Added value: +{
+  "type": "string"
+}
```
addedOutput schema / properties / hostname_matches
```
Added value: +{
+  "type": "boolean"
+}
```
addedOutput schema / properties / trusted
```
Added value: +{
+  "type": "boolean"
+}
```

changedOutput schema / required

Previous value: -[
-  "host",
-  "port",
-  "subject_alt_names",
-  "expired",
-  "expires_soon"
-]New value: +[
+  "host",
+  "port",
+  "subject_alt_names",
+  "expired",
+  "expires_soon",
+  "trusted",
+  "hostname_matches"
+]

First observedv1.0.0Jun 8, 2026

TDQS

A4.5/5.0

Behavior5/5

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

Annotations already declare readOnlyHint, idempotentHint, and openWorldHint. The description goes further by disclosing important behavior: untrusted certificates are still inspected and reported, never silently passed, and unreachable hosts or missing certificates produce errors. This meaningfully informs the agent beyond the annotations.

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?

The description is cleanly organized into Args, Returns, Example, and Errors sections with no filler. Every block earns its place, and the minor duplication of parameter wording does not harm readability.

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?

It covers parameters, return fields, a concrete example, error behavior, and the edge case of untrusted certificates. With an output schema present and annotations covering the safety profile, nothing needed to invoke this tool correctly 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%, so domain, port, and response_format are already fully documented in the schema. The description's Args block mostly restates the schema rather than adding new semantic detail, so the baseline of 3 is appropriate.

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 opens with 'Inspect the TLS certificate served by a host' – a specific verb plus a concrete resource and even lists the exact certificate fields. It is immediately recognizable as a certificate inspection tool and is distinct from the email, DNS, and HTTP-header sibling tools.

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?

It provides a clear, actionable example ('When does github.com's certificate expire?') that demonstrates the intended use case. It does not explicitly name alternatives or say when not to use this tool, so it stops short of full routing guidance.

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