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

With annotations already declaring readOnlyHint=false, destructiveHint=true and openWorldHint=true, the description usefully clarifies that no existing record is modified and states default ownership behavior. However, it says nothing about duplicate-contact handling or side effects that would justify destructiveHint=true, and with no output schema it does not say what is returned (the created contact and its id).

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 short sentences, front-loaded with the WRITE marker and the resource, with the non-obvious name mapping second and the defaults last. No filler and nothing important buried.

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 an 18-parameter mutation with no output schema, the description covers the action and two subtle field mappings but omits the return value and any failure/precondition notes. An agent can call it, yet still does not know what comes back or how to handle an existing duplicate.

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%, and the schema already documents name as company name/last name, first_name as first name/name addition, and the owner_id/user_id defaults. The description's person-name mapping and default ownership restate the schema rather than adding new semantics, so baseline 3 applies.

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?

"WRITE: create a new contact (company or person) in bexio" gives a specific verb, resource and scope in the first few words. It is trivially distinguishable from the read siblings (bexio_get_contact, bexio_list_contacts) and from the other create siblings by naming the resource.

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 "WRITE:" prefix and "Nothing existing is changed" make the mutation-vs-read distinction explicit, which is the main routing decision among these siblings. It stops short of exclusions or advice on when NOT to use it (e.g. checking for an existing contact first), so it does not reach the top band.

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