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

Goes well past the annotations: exact-match uniqueness on the trimmed company name, duplicate calls are rejected and leave no record, DATEV debtor number auto-assigned and not choosable, VAT ID not validated, no invoice created, no email sent. The rejection-on-duplicate behavior is consistent with idempotentHint=true and destructiveHint=false.

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?

Purpose is front-loaded in the first clause, then each following sentence delivers a distinct behavioral fact (uniqueness, numbering, validation, scope boundary, side-effect boundary). No sentence merely restates the tool name or the schema.

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?

Covers creation semantics, duplicate handling, and side-effect boundaries for a 9-parameter mutation tool with no annotations beyond hints. The notable gap is the return value: with no output schema, it never says whether the response contains the customer ID or the assigned DATEV debtor number, which an agent would likely need for follow-up calls.

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 100%, so the baseline is 3; the description adds real meaning on top by specifying that companyName is trimmed, exact-compared and unique in the account, and that vatId is stored verbatim without a format check. Address sub-fields (street, city, state, postalCode, country, addressLine2) are only summarized as 'an address' and left to 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?

States a specific verb and resource (create a customer record) plus the minimum required input and which fields are optional. It also explicitly separates itself from create_invoice, so an agent can route without opening the sibling's 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 a concrete when-to-use case ('store a client before their first invoice') and an explicit when-not/alternative: create_invoice does not require this tool first, because it creates the customer record itself. That is exactly the routing information an agent needs between two overlapping siblings.

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