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

Annotations already declare readOnly/idempotent/non-destructive/openWorld, so the safety bar is low. The description still adds real value: it states no login is required and that it works on public domains only, and it lists the return fields (validity, issuer, subject, expiry, days remaining, SANs, TLS version) in the absence of an output schema.

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?

Three short sentences, front-loaded with purpose, then triggers, then scope/access constraint. Every sentence carries information; nothing is restated.

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?

For a single-parameter read-only lookup with no output schema, this covers purpose, invocation triggers, expected return data, and the no-auth/public-domain scope. 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.

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

Schema coverage is 100% and the schema already documents the single 'domain' parameter with a format example. The description adds a semantic constraint the schema lacks — the value must be a public domain and no authentication is needed — which meaningfully bounds what to pass.

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?

States a specific verb and resource ('Check the SSL/TLS certificate for a domain') and enumerates what it returns, which cleanly separates it from siblings like check_security_headers, check_uptime, or check_blacklist. An agent can route to it without opening the schema.

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?

Gives concrete triggering conditions: customer asks about HTTPS, SSL errors, certificate warnings, or an expiring certificate. It stops short of naming alternatives (e.g. use check_security_headers for HSTS/CSP), so there is no explicit exclusion guidance, but usage context is clear.

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