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

The description adds significant behavioral context beyond the annotations. It explicitly states the tool takes no arguments, always returns a specific JSON structure (including keys), never raises protocol errors (returns error objects instead), and declares the operation read-only and idempotent with retry safety. This is a gold standard in transparency, especially since annotations already confirm readOnlyHint and idempotentHint.

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 concise and well-structured. It uses a front-loaded format with a bolded note on the key value proposition ('FREE'), immediately followed by the no-arguments input, return structure, usage guidance, exclusions, and error behavior. Every sentence adds unique value with no redundancy or wasted words.

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?

Given the tool's zero complexity (no params, simple output schema), the description is fully complete. It covers input, output, usage context, error handling, behavioral safety, and sibling differentiation. The presence of an output schema reduces the need to describe return values, and the description still mentions the key and structure for convenience.

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 description explicitly states 'Takes no arguments' for a schema with zero parameters. Schema coverage is 100%, so the baseline is 3. The description goes further by clearly explaining that there are no inputs, which prevents the agent from trying to pass arguments. A score above 3 is justified because the description provides absolute clarity.

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 that this tool explains 'how to unlock full personas, paid skills, and kits' and is FREE. The verb 'explain' and the specific resources (personas, skills, kits) are well-defined, and the sibling tools like get_full_persona and list_kits are implicitly distinguished as they cover individual items or pricing, not the upgrade path.

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 explicitly says 'Use when a premium tool has been refused or the caller asks what a plan covers' and provides a clear negative case: 'Not for per-bundle or per-product pricing' with named alternatives (list_kits, preview_product). This gives the agent excellent guidance on when and when not to use this tool.

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