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

Adds substantial non-obvious behavior beyond the annotations: zero cost, a link-based user flow, an implicit key-creation side effect, and the exact 'Authorization: Bearer <key>' header the user must install, plus the security guarantee that the link never reveals the key. The one gap is repeat invocation — annotations declare idempotentHint=false, so a second call presumably mints another link/key, which the description never warns about.

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?

Four short sentences, front-loaded with the cost and the core action, then the edge case, then the security caveat. Every sentence carries information the agent needs to relay to the user.

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?

With no input parameters, no output schema and no nested structures, the description carries the full burden and discharges it: it describes the return value (a link), the user action required, the fallback key-creation flow with the exact header syntax, and the security boundary. Sufficient for an agent to act and to instruct its user correctly.

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 takes no parameters, so there is nothing for the description to disambiguate; baseline 4 applies. Nothing in the text conflicts with the empty 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?

States a specific verb and resource ('add card credit to the key on this connection') and immediately clarifies that the actual credit-adding is done by the user via a returned link, not by the call itself. This differentiates it cleanly from the sibling lookup tools (domain_*, ip_lookup, etc.), which are all read-only information services.

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 makes the situation in which to use it clear: when the user needs credit, and the no-key case has explicit handling instructions. It does not state when not to use it or name an alternative path, but no obvious sibling competes for this job.

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