check_user_exists_by_phone

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

Annotations already declare readOnlyHint=true and destructiveHint=false, so the safety profile is known. The description adds no additional behavioral details such as side effects, permissions, or return format. The note about workspace_id is parameter guidance, not behavioral transparency. It does not contradict annotations, but does not enrich them beyond the obvious read-only nature.

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 efficient, leading with the primary purpose and following with a parameter hint. It avoids unnecessary words and front-loads the essential information, making it easy for an agent to parse quickly.

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 that an output schema exists (not shown but indicated), the description does not need to explain return values. Annotations cover the read-only and non-destructive nature. The description adequately covers how to obtain workspace_id and clarifies the tool's purpose. It lacks explicit alternative guidance, but for a simple existence check it is sufficiently complete.

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 coverage is 0%, so the description must compensate. It explains workspace_id by telling the agent to get available IDs from list_workspaces(), and provides an example format for phone_number (e.g. "+1234567890"). This gives meaningful context for both parameters, though it doesn't detail validation rules or accepted formats beyond the example.

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's function: 'Check whether a user account with the given phone number exists' with a concrete example. It identifies the exact resource (user account) and the specific attribute (phone number), making it distinguishable from the sibling tool check_user_exists_by_email.

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 does not explicitly state when to use this tool versus alternatives like check_user_exists_by_email. It does provide a helpful hint for the workspace_id parameter (get IDs from list_workspaces()), but no guidance on selection criteria between related tools. The purpose is clear, but usage context is minimal.

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