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

Beyond the annotations' readOnly/idempotent profile, it discloses non-obvious behavioral caveats: the invoice count and list can be incomplete, they include drafts and credit notes, and linking happens by exact company name at create/edit time. This is exactly the kind of limitation an agent could not infer from structured fields.

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 the return payload, then usage, then the completeness caveat — the ordering is logical and nearly every clause carries information. It runs slightly long, and the explicit 'Read-only.' sentence largely restates the annotations.

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 carries the full burden of describing return shape, and it does so field-by-field including the embedded recent-invoice list. An agent has enough to decide, call, and interpret results correctly.

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% and the schema already states the id comes from list_customers, so the description's main addition is the negative constraint that lookup by name is impossible. That is useful but the parameter itself needs no further syntax or format detail.

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 ('returns one customer record in full') and enumerates exactly which fields come back plus the embedded invoice count and 10 most recent invoices. This clearly distinguishes it from list_customers, get_invoice, and list_invoices.

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?

Names two concrete downstream uses: supplying recipient fields for create_invoice (explicitly noting that tool takes fields, not a customer id) and checking stored values before update_customer. It also names the precursor (list_customers) and gives an alternative path (list_invoices filtered by recipient name) for completeness.

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