Get contact

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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false, so the description's statement that it 'changes nothing' and 'never contacts a mail server' adds context beyond annotations. It also discloses the case-insensitive matching and the empty-answer behavior for unknown contacts, which are useful behavioral traits not covered by annotations.

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 concise, front-loaded with the core purpose, and every sentence adds meaningful information. It covers purpose, usage, behavior, and edge cases without redundancy.

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 (2 params, 100% schema coverage, output schema present, annotations provided), the description is complete. It covers identification methods, usage context, behavioral guarantees, and edge-case handling. No significant gaps remain.

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%, so the schema already documents both parameters well. The description adds value by explaining the mutual exclusivity ('name exactly one of the two') and the address format (address alone, not with display name), which goes beyond the schema's descriptions. It also clarifies the case-insensitive matching and the empty-answer behavior for unknown contacts, which are useful behavioral traits not covered by annotations.

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 reads one person from MailFathom's contact book, identified by contactId or address. It distinguishes from siblings like list_contacts (listing) and create_contact/update_contact (writes), and explicitly notes it reads local state only.

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?

Provides explicit guidance on when to use the address form (to answer who a message is from or who an address belongs to) and clarifies that exactly one of the two parameters must be named. It also explains the behavior for unknown persons (empty answer, not error), which helps the agent decide when to call this tool.

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