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

The description discloses that the tool takes no arguments, returns a specific JSON structure, and explicitly states it is read-only and idempotent. It also details error behavior: 'it never raises a protocol error — it returns {"error": "<what is wrong and how to fix it>"}, and assures that after correcting input it is safe to retry. This adds significant context beyond the annotations (which already mark readOnlyHint, idempotentHint, destructiveHint=false) and fully characterizes the tool's behavior.

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 very concise, with three short paragraphs covering purpose, usage, and behavior/error handling. It front-loads the core purpose in the first sentence, then adds return structure and usage guidelines without any filler. Every sentence earns its place.

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 has zero parameters, detailed annotations, and an output schema, the description is complete. It explains the purpose, when to use, error handling, and behavioral guarantees. There are no gaps left for the agent to infer. The output schema already documents the return format, so the description need not repeat it in full detail.

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 no parameters (input schema is empty), so the description does not need to add parameter semantics. The baseline is 4 for zero-parameter tools, and the description adds value by confirming that 'Takes no arguments' and specifying the exact return structure, which helps the agent understand the tool's complete interface.

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 the tool explains how to unlock full personas, paid skills, and kits, and that it's FREE. The verb 'explain' combined with specific resources (full personas, paid skills, kits) and scope (upgrade path) distinguishes it from sibling tools like list_kits, preview_product, or get_full_persona which focus on listing or getting details, not explaining the upgrade process.

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.' It also specifies when not to use it: 'Not for per-bundle or per-product pricing' and names sibling alternatives list_kits, preview_product. This provides clear context and exclusions, making it easy for an agent to decide when to invoke this tool.

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