Update a contact

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

Annotations declare readOnlyHint=false and destructiveHint=true, which aligns with this being a mutating update. The description adds critical behavioral detail beyond the schema and annotations: 'Only supplied fields change' clarifies partial-update semantics, and 'Tags replace the existing list rather than merging, so retained tags must be included' warns of a non-obvious replace behavior. This is genuinely useful and not visible in the input schema.

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, tightly written, with the most important operational warning (tags replacement) stated explicitly. No fluff, no repetition of schema details, and the partial-update semantics are front-loaded.

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 mutating CRM update tool, the description explains the key non-obvious behavior: partial updates and tag replacement. It doesn't explicitly mention return values, but an output schema exists, so that burden is reduced. It also doesn't mention auth requirements or required permissions, but the annotations already indicate a destructive operation. The description is complete enough for correct invocation assuming the agent has contactId and desired fields.

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 0%, so the description must compensate. It doesn't describe individual parameters, but it gives crucial semantic guidance about the tags parameter and the overall partial-update behavior. Since there are 8 parameters and only tags behavior is clarified, the description does not fully compensate for the missing schema descriptions, but what it does say is valuable.

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?

States a specific verb and resource ('Update a CRM contact') and distinguishes itself from siblings like create_contact and delete_contact. The description's additional behavior note about tags differentiate it from other update operations within the same tool group.

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 implicitly conveys when to use it: updating an existing CRM contact, and because only supplied fields change, it is appropriate for partial updates. However, it does not explicitly name alternatives like create_contact or search_contacts, nor does it state when not to use it. The context is clear enough for an agent to select it among siblings.

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