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

Annotations already declare readOnlyHint, idempotentHint and openWorldHint, so the safety profile is covered. The description adds genuinely non-redundant behavior: per-call pricing (0.005 USDC via x402 on Base) and that failed calls are free — critical for an agent deciding whether to retry or how to budget. It stops short of describing the response shape or any rate limits.

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?

Three short sentences: data identity first, default scope second, cost third. Every sentence carries information not present in the schema or annotations, and there is no filler or repetition of the tool name.

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 only two optional parameters and no output schema, the description covers what the tool returns (a monthly index on a 2025=100 base), the default range, and the payment implications — enough to call it correctly. The remaining gap is that the response structure (e.g., per-month series vs single value) is left unspecified and there is no output schema to fall back on.

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 'from' and 'to' are already fully documented with patterns and defaults, giving a baseline of 3. The description earns an extra point by stating the resulting span of the defaults ('last 13 months'), which reconciles the two schema defaults into one concrete behavior an agent can reason about.

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 the specific resource (Statistics Norway's monthly consumer price index, KPI), its index base (2025=100), and its temporal span (1920 to latest month). That gives an agent a precise picture of the data returned. It does not explicitly contrast itself with the sibling adjust_by_cpi, so differentiation is implied by resource rather than stated.

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?

The description supplies the default window ('last 13 months') and the cost model, which helps an agent decide whether a call is worth making. However, it never says when to use this raw index versus the sibling adjust_by_cpi, nor any prerequisites (e.g., wallet/auth for x402). Usage is implied by the data type alone.

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