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

Annotations already declare readOnlyHint=false, destructiveHint=false, and idempotentHint=false. The description adds useful context that the link is single-use, expires soon, and costs nothing, but it does not explain what state is created by returning the link, auth requirements, or what happens on reuse.

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 response is short and front-loads the core action, but the last two sentences are fragmented and ambiguous ('They type the email. Sign in with email.') without a clear referent. Not every sentence earns its place cleanly.

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?

This is a simple zero-parameter tool with an output schema and annotations, so much detail is carried elsewhere. Still, the description does not explain how the link relates to 'starter credit' or whether the caller must already be signed in or supply an email externally.

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?

With zero parameters, the baseline is 4. The description does not document parameter meanings because none exist, though 'They type the email' introduces an external action that is not represented in the schema and slightly muddies the zero-parameter design.

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 first sentence gives a specific verb ('Returns') and resource ('one link the person opens to verify their own email'), so the core action is identifiable. However, it never connects the link to the title's 'starter credit' or contrasts it with any sibling tool, so it stops short of 5.

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?

Usage is only implied: the link is for email verification and works once. There is no explicit when-to-use guidance, no alternatives, and no prerequisites; 'They type the email. Sign in with email' is ambiguous rather than actionable guidance.

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