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

With no annotations present, the description carries the full behavioral burden and does disclose the non-obvious commercial mechanic: $0.005 USDC per call via x402 with a free first daily call. It also shows the response shape. What is missing is data freshness/update lag, error behavior, and any auth/credential requirement beyond payment.

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 the resource and its outputs, then pricing, then a concrete example. The embedded JSON example is verbose but justified since there is no output schema. Every sentence earns its place; no filler.

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 single-optional-parameter read tool with no output schema, the description supplies the return structure via example, names the data sources, and discloses cost. It stops short of stating refresh cadence or whether history is returned newest-first, which would matter to an agent assembling a report.

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 the single parameter carries its own description with a default ('Months of history (default 12)'), so the schema does the work. The description never mentions the months parameter at all, adding nothing beyond the schema baseline of 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?

Names a specific resource with source attribution ('Brazilian official inflation (IPCA, IBGE via BCB)') and enumerates exactly what is returned: latest monthly change, 12-month accumulated, and monthly history. This is clearly distinguishable from siblings like selic_rate or ptax_exchange_rate without opening any 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?

Usage is implied by the data domain rather than stated; there is no explicit guidance on when to prefer this over selic_rate or ptax_exchange_rate, nor any prerequisites. The pricing note ('first call per tool per day is free') does give a pragmatic reason to call this tool sparingly, which is a mild form of usage guidance.

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