check_reverse_dns

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

Annotations already indicate readOnly, idempotent, and non-destructive, so the bar is lower, but the description adds substantial behavioral context: it discloses how the verdict is derived, defines the three possible verdict values, and warns that a bare PTR proves nothing because the IP owner controls the reverse zone. This goes well 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.

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

The description is long but every sentence earns its place: usage trigger, mechanism, verdict definitions, the PTR caveat, the fix ownership note, and the parameter requirement. The most decision-relevant information is front-loaded in the first sentence.

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

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

There is no output schema, so the description carries the burden of explaining return values, and it does: the verdict field and its three possible values are defined with their semantics. It also covers the key operational caveat and where the fix is made, making the tool fully understandable without additional documentation.

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

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

Schema description coverage is 100%, so the schema already documents the ip parameter fully, including the requirement that it be a public IPv4 or IPv6 address. The description adds the phrase 'sending IP' and clarifies the parameter's role in FCrDNS, but this is marginal value over the schema.

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

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

The description names a specific verb and resource: 'Check one sending IP's forward-confirmed reverse DNS (FCrDNS).' It also explains the core behavior, reading the PTR record and resolving it back, which clearly distinguishes it from any sibling DMARC, SPF, or DKIM tools even without naming one.

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

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

The opening line explicitly states when to use the tool: when the user asks about reverse DNS, PTR records, or FCrDNS for a mail server IP. It does not explicitly name an alternative tool or state when not to use it, but the triggering conditions are clear enough to route an agent correctly.

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