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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint=false, so the safety profile is covered. The description adds conditional behavior beyond the schema: with an API key it also reports whether the account is already on Pro and whether a free trial is available, which is genuinely useful context for an agent.

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 tightly written sentences with no filler, front-loading what is listed and then layering the conditional behavior and the sequencing advice.

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?

No output schema exists, so the description carries the burden of describing returns, and it does so reasonably: price, billing, duration, Pro status, and trial availability. A bit more on the shape/format of plans would make it fully complete.

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?

Zero parameters, so the baseline is 4. The description's note about API-key-dependent account status is the only parameter-adjacent nuance, and it correctly implies no required inputs.

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?

The description states the specific resource and its contents: current Pro plans with price, billing, and duration. It's clear this is a read/list operation on the plans catalog, though it never uses an explicit verb like 'lists' and doesn't differentiate itself from sibling list_* tools beyond the resource name.

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?

'Use before prepare_upgrade' gives explicit sequencing guidance naming the downstream sibling tool. There is no when-not guidance or statement of alternatives, but the intended call point is clear.

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