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

Annotations already declare readOnly, idempotent, non-destructive, closed-world behavior, so the safety profile is covered. The description adds genuinely non-obvious domain rules beyond that: top-up checks are consumed only after the monthly allowance, do not reset on the 1st, and expire 12 months after purchase, plus the free-tier `can_buy=false` condition.

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?

A single dense sentence covering the resource, the key output field, and three spending rules, with the catalog/balance purpose front-loaded. The parenthetical about `packs` is slightly cryptic in isolation, but no clause is wasted.

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, return values need no explanation, and with zero parameters and a read-only annotation profile, the remaining burden is domain rules, which the description supplies (allowance ordering, no monthly reset, 12-month expiry, free-tier restriction). Nothing an agent needs in order 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?

The tool takes zero parameters, so there is nothing for the description to disambiguate and the baseline applies. It does helpfully explain one output field (`packs` = live list with prices) rather than a parameter, which is a small bonus but outside this dimension's scope.

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: top-up packs for AI citation checks plus this account's balance, and names the `packs` field as the live price list. An agent can tell it is a read of pack catalog and balance rather than a purchase action, though it never names the checkout sibling explicitly.

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 rather than stated: the mention that `can_buy` is false on the free tier signals this is the pre-purchase inspection step, but there is no explicit 'use this before citation_topup_checkout' or when-not-to-use guidance. The agent must infer the workflow position.

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