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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so the safety profile is covered. The description adds meaningful behavior beyond that: no payment, a trimmed subset of items, and gating metadata (access, items_hidden, gated_fields, buy_with) that tells the agent the result is incomplete and how it is limited. Listing individual return fields is partly redundant with the output schema, which keeps it off a 5.

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 purpose and the get_cpi comparison are front-loaded and the gating fields are grouped efficiently in one clause. The trailing 'CPI ids: US, UK, EA, JP' repeats the schema enum and the sentence is long/run-on, costing a point.

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?

An output schema exists, so return values needn't be explained, yet the description adds the crucial caveat that output is truncated and gated. For a one-parameter read tool with rich annotations, nothing an agent needs to call it correctly is missing.

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% and the single parameter already has an enum and description, so the schema carries the load. The description restates the id values ('CPI ids: US, UK, EA, JP'), which is duplication rather than added meaning; only 'covered country or area' adds nuance. Baseline 3 applies.

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 — a free sample of the latest inflation (CPI) card — and scopes it precisely ('trimmed view', no payment). It explicitly names the sibling it differs from ('test before paying for get_cpi'), so an agent can route without opening either 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?

Gives an explicit use case (evaluate before paying) and names the alternative tool (get_cpi) that applies once the agent commits. The when-to-use vs. when-to-upgrade decision is fully stated, not implied.

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