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

Annotations cover safety (readOnly, idempotent, non-destructive), and the description adds genuinely non-derivable context: a $0.01 paid call, two auth paths (api_key vs x402), and a staleness caveat that a later gazette can silently retire a value, which motivates following up with get_changes or register_alert. The follow-up push costs are informative, though slightly promotional in tone.

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 the paid price and the core scope, then packs payment mechanics and follow-up guidance into dense clauses. It is long for a two-parameter tool and the parenthetical price list ('Register: $0 · Delivery after trial: $0.05') is clutter, but nearly every clause carries actionable information.

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?

With an output schema present, the description need not restate return values, yet it still summarizes the returned fields. It covers cost, both authentication paths, the staleness risk, and the recommended follow-up tools, leaving no obvious gap for correct invocation.

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 the country enum already documents itself; the baseline would be 3. The description goes beyond the terse schema description for api_key ('API key') by explaining what happens with and without one, adding real meaning for the weaker of the two parameters.

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 ('Country brief: every reference series we hold for one country') and enumerates the contents (policy rate, VAT/GST, CPI, taxes, minimum wage, holidays) plus the per-series fields returned. This clearly distinguishes it from siblings like get_series and list_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?

It contrasts itself with the alternative ('Cheaper than buying the series one by one'), implicitly routing the agent away from individual series calls, and gives concrete prerequisites for payment (pass api_key, or the response explains x402). It stops short of an explicit when-to-use/when-not rule, but the context is clear.

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