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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint=false, but the description goes further: it explains that errors never surface as protocol errors but as {"error": ...} objects with a fix hint, and that retry after correction is always safe. That error-contract detail is exactly the kind of behavior annotations cannot express.

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?

Purpose and the "FREE" qualifier are front-loaded, and the alternative-tool routing follows immediately. The middle sentence restates the single-skill selection already implied, which is mild redundancy but the structure stays scannable.

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 one-parameter read tool with an output schema, the description still covers return shape, error contract, plan prerequisites, and sibling routing. Nothing an agent needs to call it correctly or recover from failure 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?

Schema coverage is 100% and the slug parameter is already documented, so the baseline would be 3; the description earns extra credit by pairing a concrete input example with its output shape and by reinforcing where the slug comes from (list_products). It stops short of 5 because no additional slug-format edge cases are given.

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?

States a specific verb and resource ("Load a product's free gateway skill with its complete instructions") and explicitly distinguishes itself from get_full_skill, which serves the product's other skills. An agent can pick the right tool without opening either schema.

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?

Names the selection condition ("Use when the caller wants usable instructions immediately") and the exclusion ("Not for the product's other skills: those are named and need get_full_skill with a skill_name, which requires a paid plan"). Both the when and the when-not are explicit, plus the prerequisite difference (no plan vs. paid plan).

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