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

The annotations already indicate readOnlyHint=false, destructiveHint=false, and idempotentHint=true, so the safety profile is known. The description states 'update' which aligns with these annotations, but it does not add context such as whether updates are reversible, what happens if fields do not exist, or any side effects beyond the operation itself.

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, direct sentence with no filler. It is efficient and front-loads the essential purpose without unnecessary detail.

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 relatively simple tool with full schema coverage and informative annotations, the description is sufficient for an agent to invoke the call correctly. It might benefit from a note on partial field updates or error behavior, but the current form is mostly 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 description coverage is 100%, with each parameter (fields, api_key, contact_id) already documented in the input schema. The description adds no extra meaning beyond the schema, so the baseline score of 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 is clear: 'Update fields on an existing contact' uses a specific verb, resource, and scope. It distinguishes this tool from siblings like create_contact and delete_contact by explicitly stating 'update' and 'existing', though it does not elaborate on what specific fields can be updated.

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?

No guidance is provided on when to use this tool versus alternatives such as update_contact or create_contact. There is no mention of prerequisites, edge cases, or situations where a different tool would be more appropriate. The intent is largely left to inference from the tool name.

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