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

Annotations already declare readOnlyHint=true, destructiveHint=false, and idempotentHint=true. The description adds context about the data source (BCB SGS) and series number, but does not contradict annotations. For a read-only tool, this is adequate but not exceptional.

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 extremely concise at one line, front-loads the key information (what, where, series, license), and contains no wasted words. Every sentence earns its place for a simple data retrieval tool.

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's low complexity (one optional param, output schema present) and the fact that the schema covers the param description, the tool description provides sufficient context: data source, series, and license. It is complete for the intended use.

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?

Input schema coverage is 100%, and the schema already describes last_n with details (range, default, note on daily vs monthly). The description adds no further parameter information, so baseline 3 is appropriate.

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 identifies the tool as returning the Brazilian SELIC daily interest rate (series 11) from the BCB SGS system. It specifies the resource and action, though the verb 'get' or 'retrieve' is implicit. It distinguishes from sibling tools like finance.bcb.selic_target or finance.bcb.cdi by noting the specific series.

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?

No guidance is provided on when to use this tool versus alternatives. It does not mention scenarios where other BCB tools (e.g., for CDI, IPCA, or SELIC target) would be more appropriate, nor does it note prerequisites or context.

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