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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint, so the safety profile is covered. The description adds valuable beyond-annotation context: listing plans never starts a checkout or charge, prices are integer minor currency units, and prices are server-configured.

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 sentences, all high-signal and front-loaded with the primary use case. No filler or repeated schema/annotation information.

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 parameterless read-only listing tool, the description covers when to use it, what it returns conceptually, and what not to do with the output. It does not explicitly mention whether an account connection is required, but the sibling set and checkout context imply it is a lightweight pre-checkout lookup.

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 has zero parameters, so the baseline is 4 and there is nothing for the description to clarify. The description still usefully defines the return semantics in terms of exact server-configured prices and plan identifiers.

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 uses a specific verb and resource: listing CongressMCP subscription plans and showing exact server-configured prices. It clearly distinguishes itself from checkout creation by stating it never starts a checkout or charge, and the sibling set makes the contrast with create_subscription_checkout obvious.

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?

It explicitly says to use this tool before checkout, which is the key trigger condition, and warns against guessing prices or using plan identifiers not returned here. It does not explicitly name the alternative checkout tool, but the timing and negative instructions make the intended usage clear.

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