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

Goes well past the annotations (which only say non-readonly, non-destructive, closed-world) by disclosing that the key is shown once and is unrecoverable, the return fields (key, connect, next, plus email vs anonymous), the failure cases ('an email already signed up, or not an email, says so'), and the rate limit ('three an hour from one address'). It even flags that a throwaway key has a reduced read allowance.

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?

Labeled lines (When / Instead / Inputs / Returns / Fails) make it skimmable and front-loaded, with no filler sentences. The occasional garbled phrase ('the person's by email', 'reads and asks for a few reads an hour') costs a little clarity but no whole sentence is wasted.

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?

There is no output schema, yet the description enumerates the returned fields (key, connect, next, and whether the key is email-tied or anonymous), states the one-chance display constraint, lists failure modes, and gives the rate limit. An agent has everything needed to call it and to decide what to do on success or failure.

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 schema already says almost verbatim that email is the person's address and should be omitted for a throwaway key. The description reinforces the effect of omitting it but adds no new syntax, validation, or format detail beyond the schema — baseline 3 is appropriate when the schema does the work.

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 ('Gets a free key, shown once') plus the immediate follow-on artifact (the connect command), and distinguishes the two issuing modes (by email vs throwaway). It also names the sibling it is not — clickd_claim — so an agent can separate key issuance from site claiming 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?

Explicit 'When: when a call needs a key and there is none' covers the trigger, and 'Instead: clickd_claim, with a person's key, to make a site theirs' names the alternative and the condition that selects it. It also states a precondition ('Needs no key'), which is exactly the routing information an agent needs.

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