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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint, but the description adds meaningful behavioral context beyond them: it never raises a protocol error on invalid/missing/malformed input and instead returns an error object. It also states that every call is read-only and idempotent, making retry safety explicit.

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 front-loaded with the core purpose ('Explain how to unlock full personas, paid skills, and kits'), then moves to return shape, usage context, exclusions, and error behavior. Each sentence earns its place and the structure is logically ordered.

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?

The description covers the return shape, the exact use case, exclusions, error behavior, and safety profile. There is an output schema, but the description still explains the key return fields and retry semantics. Nothing an agent needs to call this tool 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 has zero parameters, and the description explicitly says 'Takes no arguments.' It also explains that invalid or malformed input will yield a structured error response, which is useful even for a no-argument tool. Since the schema is empty, this description fully covers parameter semantics.

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 a specific verb and resource: 'Explain how to unlock full personas, paid skills, and kits.' It also clearly differentiates from siblings by explicitly excluding per-bundle or per-product pricing and naming list_kits and preview_product as the alternatives. An agent can recognize exactly what this tool is for without opening schemas.

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?

The description gives explicit when-to-use guidance: 'Use when a premium tool has been refused or the caller asks what a plan covers.' It also states what it is not for, naming sibling tools list_kits and preview_product. This fully routes the agent between alternatives.

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