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

Annotations already declare readOnlyHint and idempotentHint, so the safety profile is known. The description adds value by specifying the exact information returned (remaining quota, reset date, upgrade path), which is beyond what annotations provide. It doesn't mention troubleshooting or edge cases, but for a simple status check this is sufficient.

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, with the primary purpose front-loaded. The first sentence states exactly what the tool does; the second adds actionable context for users without a key. No 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?

The tool has an output schema (not shown here), so return values need not be described. The description covers the purpose, the required parameter, and the alternative for keyless users, making it complete for a simple read-only operation.

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% for the apiKey parameter, with the schema already noting 'free-tier key (hp_free_...)'. The description repeats this format ('hp_free_ key') without adding new semantic meaning. Thus the baseline of 3 applies.

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 the resource ('free API key's remaining monthly quota, reset date, and upgrade path'). It is unambiguous and distinguishes this tool from the listed siblings, none of which deal with free-tier 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 explains when to use the tool (when you have a free API key) and provides explicit guidance for those who don't ('No key yet? POST an email to https://hermesplant.com/api/keys/free'). This serves as a clear when-to-use and when-not-to-use (since the tool requires an existing key).

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