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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint, indicating safe read-only behavior. The description adds value by explicitly stating 'Read-only' and requiring a connected account, which is a behavioral constraint not present in annotations. This provides additional context beyond what annotations offer.

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 concise sentences with no redundant words. The primary purpose is stated first, followed by a usage hint and prerequisite. Every sentence earns its place.

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?

Given the tool's simplicity (no parameters, no output schema, no nested objects), the description completely covers its function, output preview, prerequisite, and place in a larger workflow. No additional information is necessary for correct invocation.

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 has zero parameters, so the input schema fully documents them (100% coverage). The description does not need to add parameter semantics, and stating the return info (name + contact count) indirectly clarifies the output. The baseline for no parameters is 4.

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 uses a specific verb ('List') and resource ('your saved distribution lists') and specifies what information is returned (name + contact count). It also explains the tool's purpose in the workflow: to pick one to invite from with send_invitations. This distinguishes it from sibling tools like list_guests or list_contacts.

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 clearly states when to use the tool ('so you can pick one to invite from with send_invitations') and includes a prerequisite ('Requires a connected account'). It does not explicitly mention when not to use it or provide alternatives, but the context is sufficient for choosing this tool over others.

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