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

Annotations already declare readOnlyHint, openWorldHint and idempotentHint, so the safety profile is covered. The description adds genuine value beyond them by inventorying the payload an agent will receive (current price, validity, requirements, mandatory order fields, URLs), which substitutes for the absent output schema. It does not cover not-found/error behavior, which would be a nice addition.

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?

A single front-loaded sentence: verb, resource, lookup key, then a compact colon-separated inventory of return fields. No filler, nothing to trim.

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 one-parameter read tool with full annotation coverage, the description is nearly sufficient: it explains the lookup key and enumerates the return content in place of a missing output schema. It stops short of describing failure modes (invalid/unknown slug) or routing to search_products.

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% and there is only one parameter, whose schema entry already explains the slug with an example ('e-cpf-a1-12m'). The description's 'pelo slug' adds nothing beyond the schema, so the baseline 3 applies.

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 ('Detalha um certificado') plus the lookup key ('pelo slug'), and enumerates the facts returned (price, validity, requirements, required order fields, URLs). Clear on its own, but it never distinguishes itself from the sibling search_products, so an agent must infer the read-detail vs. list distinction.

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 gives no when-to-use statement, no prerequisites, and no mention of alternatives. With search_products as a sibling, the obvious question of whether to browse or fetch a single product by slug is left entirely to inference; only the required 'slug' argument hints at post-search usage.

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