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

Annotations already declare readOnlyHint and openWorldHint, so safety is covered. The description adds genuinely valuable context beyond annotations: the per-call price ($0.002 USDC via x402) and that failed calls are not charged. That is exactly the kind of behavioral detail an agent needs before invoking a paid tool.

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-loads what the tool returns, then catalogue guidance, then pricing. Efficient, no filler. The inaccurate default figure is a flaw, but the structure itself is tight.

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?

Output schema exists, so return shape needn't be explained; the description covers source, pricing model, and catalogue reference. The lingering gap is the default-count mismatch, which slightly undercuts completeness for a paid tool where the agent must trust the description.

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% for the two parameters, so the baseline is 3. However the description says the latest-N default is 12 while the schema says 'default 5', an internal inconsistency that could mislead. The mention of dates/values is return-focused, not parameter-explanatory.

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: 'latest N values of one series number' from the BCB SGS time series, with dates and values. This clearly distinguishes it from other bank/macro siblings. It stops short of naming a specific alternative sibling, but the resource is unambiguous.

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?

It tells the agent that series numbers come from the BCB SGS catalogue, which is a useful prerequisite. But it gives no explicit when-to-use versus alternatives or exclusions among the many finance data siblings. Usage is implied rather than guided.

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