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 behavioral context beyond annotations: 'No key needed' indicates authentication requirement, and it outlines the return shape (JSON with plans array, enterprise, signup_url). This adds useful operational detail without contradicting annotations.

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 description is efficient, with zero filler. It front-loads the core purpose, then immediately lists return fields and routes to alternatives. Every sentence earns its place, and the structure makes it easy to scan. It strikes a balance between completeness and brevity.

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 list tool, the description covers all necessary information: what data is returned (field names), the use case, and exclusions. Annotations cover safety, and the description provides the output structure despite lacking an output schema. Nothing an agent needs to call this 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?

There are zero parameters, so the empty schema needs no explanation. Per rubric, baseline for 0 params is 4. The description appropriately focuses on output and use cases rather than parameters, which is correct for a parameterless tool.

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 clearly states it lists public plans with specific fields (price in cents, billing interval, included units, burst rate limits, enterprise line, signup URL). It uses a specific verb 'List' and resource 'FlexYield's public plans', and explicitly differentiates from siblings by naming what it is not for (get_quote, get_billing_status, what_can_i_do). This leaves no ambiguity about scope.

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 provides explicit when-to-use: 'Use it to compare plans or before telling an owner what an upgrade costs.' It also gives explicit when-not-to-use with named alternatives for three distinct cases, covering all common misuse. This is exemplary guidance.

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