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

The description adds meaningful behavioral context beyond the annotations by stating the tool is 'Keyless' and describing the exact return payload: DNS names, issuing CA, validity window, revocation status, and a deduplicated hostname list. It also clarifies that include_subdomains enables subdomain enumeration. This supplements the readOnly/idempotent annotations without contradicting them, though it omits details like pagination or rate limits.

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 four sentences, each earning its place: purpose, usage guidance, subdomain behavior, and output summary. It is front-loaded with the primary action, immediately followed by practical use-case examples. There is no fluff or redundant repetition of the schema or annotations.

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?

Given the tool has no output schema, the description compensates thoroughly by listing all return fields (DNS names, CA, validity, revocation status, discovered hostnames). It also specifies the default behavior of include_subdomains and notes that the hostname list is always complete. This provides a sufficiently complete mental model for an agent to invoke the tool correctly and interpret results.

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?

Although the schema already has 100% coverage for parameter descriptions, the tool description adds extra semantic value. It explains that include_subdomains 'is what enables subdomain discovery' and that the discovered-hostnames list is always complete regardless of the limit. This goes beyond the schema's static descriptions and helps the agent understand the implications of parameter choices.

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 clearly states the tool's function: finding SSL/TLS certificates for a domain from Certificate Transparency logs. It uses a specific verb ('Find') and identifies both the resource (certificates) and the source (Cert Spotter), which differentiates it from other domain-related tools. It also explicitly outlines use cases like finding subdomains and checking expiration, leaving no ambiguity.

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 description provides explicit when-to-use guidance with 'PREFER OVER WEB SEARCH' and lists concrete example queries ('what certificates does X have', 'find subdomains of X'). It also explains when the include_subdomains flag is relevant. However, it does not mention when not to use the tool or alternative tools except for web search, so it lacks a full exclusion statement.

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