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

The description discloses the load-merge-write mechanism and the fact that the API is really a full replace, adding context not available from annotations alone. It also confirms the destructive side effect, matching the destructiveHint annotation without contradicting it.

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?

Every sentence earns its place: purpose, field-omission guidance, the merge mechanism, the group-name constraint, and the side effect. It is concise while covering essential behavioral and usage details.

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 the tool has an output schema and detailed parameter schemas, the description completes the picture by explaining the merge semantics and group-name constraint. It is sufficiently complete for an agent to select and call the tool correctly.

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?

The schema descriptions already carry the full parameter semantics, including the 'fields to change only' behavior and group name requirement. The prose description mostly echoes this information, so it adds little beyond the schema.

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 and resource ('partially update an existing contact') and clarifies the partial-update scope, which distinguishes it from create/delete operations. The wording leaves no ambiguity about what the tool does.

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 gives actionable guidance on how to invoke partial updates and how to handle groups. It does not explicitly contrast with related tools such as set-contact-groups or create-contact, which keeps it just below the highest bar.

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