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

Annotations already declare readOnlyHint=true, idempotentHint=true and destructiveHint=false, so the safety profile is covered. The description adds value beyond that by disclosing the payload shape (price, allowance, features, current plan) and the fact it spans both all plans and the account's own — context a no-param list tool otherwise wouldn't convey.

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?

Two sentences, zero padding. The contents come first and the usage cue second, which is the right front-loading for a listing tool.

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 no output schema, the description carries the burden of saying what comes back, and it does list the key fields plus the current-plan comparison. It does not describe ordering, pagination or whether historical/legacy plans are included, minor gaps for a no-arg static 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?

The tool takes zero parameters, so there is no parameter semantics to document; the baseline for a no-param tool is 4. Nothing in the description is needed to explain inputs, and it doesn't waste words pretending otherwise.

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 (list) and resource (Asyntai plans) and enumerates the returned content — price, monthly message allowance, included features — plus the account's current plan. No sibling tool lists plans, so it is trivially distinguishable from the surrounding add_/get_/list_ family.

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 a concrete trigger: 'Use it to explain which plan includes a feature the account asks about.' This tells the agent when to reach for it during plan/feature questions. It stops short of naming an alternative or an exclusion condition, but no competing sibling exists for this data, so the guidance is effectively complete.

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