list_contact_fields

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

With no annotations provided, the description carries the full burden. It discloses that the tool returns all built-in and custom fields with types and visibility, which is the key behavioral output. It doesn't mention side effects, but as a read-only list operation, this is adequate. It adds value beyond the empty schema by describing the return contents.

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 plus a helpful example. It front-loads the purpose in the first sentence, adds usage context in the second, and provides example queries. Every part earns its place without unnecessary verbosity.

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), the description fully covers what the tool does, what it returns, and when to use it. The example queries further aid the agent in recognizing invocation scenarios. No missing information is critical for correct use.

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, and the schema is empty. Per the rubric, a 0-parameter tool gets a baseline of 4. The description adds nothing about parameters because there are none, so no deduction is warranted.

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 'List all contact fields (built-in and custom) with their types and visibility,' using a specific verb (list) and resource (contact fields). It distinguishes from siblings like list_contacts (lists contacts, not fields) and create_custom_field (creates fields).

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?

It explains 'Useful for understanding what data you can store on contacts' and provides example queries, giving clear context for when to use it. It does not explicitly name alternatives or exclusion criteria, but the intended use is evident.

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