list_contacts

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

Annotations already declare readOnlyHint=true, destructiveHint=false, and openWorldHint=false, covering safety and scope. The description adds valuable behavioral context: the default filtering logic (only contacts you've replied to) and the override mechanism (include_all). It doesn't mention pagination or rate limits, but with annotations present, this is sufficient for a high score.

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?

Three sentences with zero waste: first states purpose and key features, second explains default behavior, third provides usage guidance. Every sentence earns its place by adding distinct value (scope, filtering logic, parameter guidance).

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?

For a read-only listing tool with good annotations and full schema coverage, the description is nearly complete. It explains the tool's purpose, default behavior, and key parameters. The main gap is lack of output format details (no output schema), but given the annotations and context, this is a minor omission. It adequately supports agent decision-making.

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 parameters are fully documented in the schema. The description mentions filtering by 'tier and minimum message threshold' and the 'include_all' parameter, but doesn't add significant semantic meaning beyond what the schema provides (e.g., it doesn't explain what 'tier' represents or how 'min_messages' is calculated). Baseline 3 is appropriate when schema does the heavy lifting.

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 verb ('List') and resource ('contacts') with specific scope ('all contacts with message counts and tier assignments'). It distinguishes from siblings like 'get_contact' (single contact) and 'resolve_contact' (identity resolution) by emphasizing comprehensive listing with metrics.

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?

Explicitly states when to use alternatives: 'By default, only shows contacts you've actually messaged (replied to). Use include_all to see all.' This provides clear guidance on the default behavior versus the override parameter, helping the agent choose between filtered and comprehensive views.

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