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

Annotations already establish readOnlyHint=true, idempotentHint=true and destructiveHint=false, so the safety profile is covered. The description adds genuinely useful semantics beyond that: flat-model users incur no credits and 1 credit = 0.01 EUR, which helps the agent interpret results. It does not describe return format or scope of the pricing table, so it stays at an adequate 3.

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 core two sentences are tight and front-loaded, but the appended 'EN: ...' keyword list is SEO-style filler that repeats concepts already present and names terms belonging to sibling tools, adding noise rather than clarity.

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 read-only, parameterless pricing lookup with no output schema, the description conveys what the agent will learn (per-operation credit costs, currency conversion, flat-user exemption). Enough to call and interpret it correctly, though it never states the shape or granularity of the returned pricing listing.

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?

There are zero parameters and the schema is an empty object, so there is nothing for the description to document; the baseline for a parameterless tool is 4.

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 resource (credit costs per action, pay-per-use) and verb-like function (show how many credits each operation consumes). It is distinguishable from onto_credit_balance, onto_credit_chargeup, and onto_credit_checkout, but the trailing 'EN: credit, balance, pricing, billing, top-up, checkout' keyword blob overlaps with those siblings' domains and muddies differentiation.

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?

No explicit when-to-use or when-not-to-use guidance, and no sibling alternatives named. The only conditional signal is the informal note that flat-billing users pay nothing, which is context rather than routing advice.

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