create_contact

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

No annotations are provided, so the description carries the full burden of behavioral disclosure. It states 'create' (implying mutation) but does not disclose side effects (e.g., whether the contact is immediately visible, if the operation is reversible, or what happens if the address book ID is invalid). It also doesn't mention required permissions or the return value. This lack of behavioral context for a mutation tool with no annotations warrants a 2.

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 a single, concise sentence that gets straight to the point. There is zero wasted text, and it is front-loaded with the core action. It is appropriately sized for a simple create tool, even though it could have added more detail without becoming overly verbose.

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?

The tool has 10 parameters, no output schema, and no annotations. The description does not mention what the tool returns (e.g., the created contact or its ID), nor does it provide any usage context beyond the basic action. While the schema covers parameter details, the lack of return-value information and any caveats leaves the description incomplete for a tool of this complexity.

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 input schema has 100% coverage of all 10 parameters, so the schema already documents each parameter's meaning. The description adds no parameter-level detail, but the baseline for high schema coverage is 3. The schema even notes that addressBookId comes from list_address_books, which is helpful, though that is in the schema, not the tool description.

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 'Create a new contact in the Fastmail address book' uses a specific verb ('create'), a clear resource ('contact'), and a context ('Fastmail address book'). It clearly distinguishes this tool from sibling contact tools like update_contact, delete_contact, and get_contact, so the purpose is unambiguous.

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 implies usage through the verb 'create'—if a user wants to create a contact, this is the tool. However, it provides no explicit when-to-use or when-not-to-use guidance, no mention of prerequisites (e.g., needing an address book ID from list_address_books), and no reference to alternatives. This is minimal but not misleading, so it earns a 3.

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