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

Annotations already declare readOnly/idempotent/non-destructive behavior, so the bar is lower, yet the description adds real context: returned fields (net return after IR, real return above IPCA) and the crucial constraint that without an API key only a short preview is returned. It stops short of describing pagination or result ordering beyond the schema's sort_by.

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?

Front-loaded with purpose, then the return semantics, then the index encoding, then the API-key caveat. Dense but each clause carries information; the encoding sentence is somewhat run-on but not wasteful.

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?

No output schema exists, so the description must carry return-value meaning, and it does by naming the two return fields and their units. With filters fully documented in the schema and safety covered by annotations, only minor gaps (ordering/pagination details) remain.

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%, so baseline is 3, but the description adds interpretation the schema does not: it decodes how the numeric 'rate' value maps onto each 'index' (cdi* 1.05 = 105% of CDI, ipca+ 0.06 = IPCA + 6% a.a.). That is genuine semantic value beyond the enum listing.

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 ('Search active Brazilian fixed-income bonds and rank them'), which is clearly distinguishable from the only sibling, list_issuers, that merely enumerates issuer codes. An agent can tell what this tool returns without reading 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?

The description explains how filters behave (rate/index encoding, preview without an API key) but never states when to choose this tool over list_issuers or gives explicit exclusions. Usage is implied via filter semantics rather than stated, which is the minimum viable level.

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