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

Beyond readOnlyHint/openWorldHint, it discloses the result cap (10 newest), the data source and its freshness model (public CT log index), the negative scope (no revocation, no live chain), and the billing model ($0.001 USDC via x402, failed calls free). That is exactly the context annotations cannot carry.

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 sentences, front-loaded with what is returned, then limits, then cost — no filler. The first sentence is dense with a parenthetical source citation, but every clause carries information.

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?

With an output schema present, the description only needs to cover scope, caps, source, and cost, and it does all four. An agent can decide whether the 10-certificate cap and lack of revocation data matter before spending money.

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?

One required parameter with 100% schema description coverage (including the 'URL is reduced to its host' normalization note), so the schema already does the work. The description adds no further domain formatting or validation detail, matching the baseline 3.

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+resource ('Recent TLS certificates logged for a domain') and names the underlying source (Certificate Transparency via Cert Spotter's public index) along with the fields returned. It does not explicitly contrast against nearby siblings like dnssec_trust_chain_validator or subdomain_takeover_monitor, so an agent must infer the boundary.

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 exclusions ('does not check revocation or the live server's certificate chain') give useful negative guidance about when this lookup is insufficient. It stops short of naming an alternative tool for those needs, which keeps it out of 5 territory.

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