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

Annotations already declare destructiveHint: true and readOnlyHint: false. The description's 'Side effects: modifies contact group.' merely restates this without adding new behavioral context (e.g., whether it's a partial update, permission requirements, or effects on existing data). It adds no value beyond the annotations.

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 extremely concise, using two short lines with no filler. The core action is front-loaded, and the side-effect note is minimal. Every word earns its place.

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 update tool with an output schema present, the description is mostly sufficient. However, it does not clarify that the update is partial (only name/notes fields) or that unprovided fields remain unchanged. Given the simplicity and that the schema already conveys the fields, a 3 reflects the slight gap in behavioral nuance.

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 clear definitions for both group_id and payload. The description adds no parameter-specific details. Per calibration, baseline is 3 when schema fully documents parameters, and the description does not enhance or compensate further.

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 verb 'Update' and the resource 'contact group', with a parenthetical 'Fax.Plus tag' to disambiguate the term. It distinguishes from create/delete/list siblings by virtue of the action, though it doesn't explicitly name them. The purpose is unambiguous and not a tautology.

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 like create-contact-group or delete-contact-group. There is no mention of prerequisites, typical scenarios, or exclusions. The description merely states the action without any usage context.

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