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

The annotations declare destructiveHint=true and idempotentHint=true, and the description earns its keep by spelling out exactly what is destroyed: 'The list replaces every period they have now ... an empty list removes them all' is in the schema, and the description reinforces the replace semantics. It also discloses the permission prerequisite and that the response is the changed contact, none of which the annotations cover.

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?

Front-loaded with purpose, then destructive semantics, then prerequisite. Every sentence carries information, though the middle sentences are somewhat dense. No filler.

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?

With no output schema, the description still tells the agent what comes back ('The answer is the changed contact') and covers the mutation semantics, permission gate, and prerequisites. Nothing needed to call it correctly is missing.

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%, so the per-field meaning is already documented (baseline 3). The description adds meaning beyond the schema by framing contact_id as coming from list_contacts and clarifying that the acc_classifications array is a full replacement rather than a patch, which changes how an agent must construct the parameter.

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 (Sets) and resource (a contractor's ACC classification periods) plus the source of truth (their ACC invoice). The replace-all semantics are stated up front, so an agent can distinguish this from update_contact or set_contact_paye_salary without opening the schema.

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?

Gives the operational approach explicitly ('start from the periods list_contacts shows and include the ones that stay, by id') and a hard precondition ('Only for an organisation where this connection may add and change records (list_organisations says which)'). It also points the agent at the two sibling tools it must consult first (list_contacts, list_organisations).

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