list_users

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

Annotations already declare readOnlyHint=true, openWorldHint=true, idempotentHint=true, and destructiveHint=false, so the safety profile is fully covered. The description adds behavioral context beyond the annotations by disclosing that pagination is automatic ('Every page is walked') and that results are keyed by userId. This is useful, non-obvious behavior that an agent would otherwise have to infer from the output schema or by trial.

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 compact and front-loaded: the first sentence states the action, resource, and return fields. The second sentence provides routing guidance and pagination behavior. Every sentence earns its place; there is no filler or repetition of schema content.

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 simple read-only list tool with one parameter, a full output schema, and comprehensive annotations, the description is nearly complete. It covers what is returned, how to select the right sibling, and pagination behavior. The only minor gap is that it doesn't explicitly state the output shape (e.g., that results are in an array), but the output schema already covers that, so the description need not repeat it.

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 fully documents the single parameter (entity). The description adds a small but meaningful clarification: the entity must be the exact `entity` key from `list_entities`, not its `display_name`, and that it is required with no default. This goes slightly beyond the schema's own description, but since the schema already covers the parameter, a baseline 3 is appropriate.

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 states a specific verb ('List'), a specific resource ('one organization's Mercury users (team members)'), and the exact fields returned (id, first and last name, email, role). It also distinguishes itself from siblings by naming list_recipients and list_customers as alternatives for different entity types, so an agent can tell them apart without opening schemas.

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 explicitly says when to use this tool ('for users and their roles') and when not to ('use list_recipients for payees and list_customers for invoice customers'). It also notes that every page is walked and keyed by userId, which is a clear usage detail. This is explicit routing guidance with no ambiguity.

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