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

Annotations already declare readOnlyHint and idempotentHint, so the safety profile is covered. The description adds useful behavioral context by specifying what the check reveals (quota, reset date, upgrade path) and the key format. It does not contradict 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 two sentences: the first clearly states the tool's purpose, and the second provides the parameter format and alternative action if no key exists. It is front-loaded, concise, and every word serves a purpose.

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 simple 1-parameter read-only tool with an output schema present, the description covers the input, the key format, and how to obtain a key if missing. No critical context 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 description coverage is 100%, as the single parameter apiKey is already described as 'Your free-tier key (hp_free_...)'. The description repeats this instruction ('Pass your hp_free_ key as apiKey') without adding new semantic details, so it adds minimal value beyond the schema.

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's function with a specific verb ('Check') and resource ('free API key'), and lists the exact outputs ('remaining monthly quota, reset date, upgrade path'). It distinguishes itself from sibling tools, which focus on analysis, validation, or purchasing, none of which relate to key status.

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 provides explicit usage context: pass your hp_free_ key as apiKey, and if you don't have a key, it directs you to a signup endpoint. It does not mention when not to use it or alternatives among siblings, but the guidance is clear and actionable.

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