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

Annotations already declare destructiveHint=true, idempotentHint=true and openWorldHint=true. The description adds one genuinely new fact — that the tag is auto-created when absent — but says nothing about what 'destructive' means here (e.g., does the tag get removed from other contacts?), permission requirements, or behavior when the contact is already tagged.

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?

A single tight sentence with the core action front-loaded and the side effect appended. No waste, though it is arguably too terse for a mutating tool with an undocumented parameter.

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 two-parameter mutation with no output schema and no annotations beyond hints, the description covers the basic action and side effect but omits return shape, error cases, and tag_name semantics. Adequate as a minimum, not 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 only 50%: 'id' is documented but 'tag_name' is a bare string. The description does not clarify whether tag_name must match an existing tag's casing, whether it is created verbatim, or any format constraints, so it fails to compensate for the coverage gap.

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 ('Puts a tag on a contact') plus an important side effect ('creating the tag if it doesn't exist'). It is clear enough to distinguish from untag_contact by name alone, but never references the sibling explicitly.

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?

There is no when-to-use or when-not-to-use guidance, and no mention of untag_contact, add_contact_to_list, or update_contact as related operations. The agent must infer the scenario entirely 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.