domain-security-mcp-server

CAA Record Check

caa_check

Read-onlyIdempotent

Check a domain's CAA records to determine which certificate authorities are allowed to issue TLS certificates, and detect if any CA can issue.

Instructions

Check a domain's CAA (Certification Authority Authorization) records — which CAs are allowed to issue TLS certificates for it. Absence means any CA may issue.

Args:

domain (string): the domain to check.
response_format ('markdown' | 'json'): output format (default 'markdown').

Returns: { found, issue[], issuewild[], iodef[] }.

Example: "Which CAs can issue certs for google.com?" -> caa_check(domain="google.com").

Input Schema

TableJSON Schema

Name	Required	Description	Default
`domain`	Yes	Domain to query, 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
`found`	Yes
`iodef`	Yes
`issue`	Yes
`domain`	Yes
`issuewild`	Yes

Schema Changelog

Changes observed during successful MCP inspections.

Changed4 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"

First observedv1.0.0Jun 8, 2026

TDQS

A4.1/5.0

Behavior3/5

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

Annotations already convey that the tool is read-only, idempotent, and non-destructive. The description adds useful domain context about CAA absence and lists return fields, but it does not disclose operational behavior such as live DNS query mechanics, caching, or resolver dependence. Given the annotation coverage, this is adequate but not exceptionally rich.

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 front-loads the core purpose, includes a one-line semantic clarification, then presents Args, Returns, and an Example in a compact, scannable structure. Every line earns its place and there is no 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?

For a simple two-parameter, read-only DNS lookup with 100% schema coverage and an output schema, the description is complete. It states the operation, explains the meaning of absent results, specifies the return shape, and provides an example mapping to the correct argument.

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?

The input schema already documents both parameters fully, including the enum and default for response_format, so the baseline is 3. The description restates the arguments and gives a helpful example, but adds no new type, constraint, or semantic detail beyond what the schema already provides.

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 and resource: 'Check a domain's CAA ... records'. It also explains the real-world meaning ('which CAs are allowed to issue TLS certificates'), making the tool's purpose unambiguous and clearly distinct from sibling DNS/email checks.

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 gives clear context for when to use the tool, including the important semantic that absence of CAA records means any CA may issue, and provides a natural-language example mapping a user query to the correct call. It does not explicitly name alternative tools or state when not to use it, but the intended use is strongly implied.

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