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

Annotations already carry the safety profile (readOnly, non-destructive), so the description earns credit for adding real context: the draft-invoice quirk ('status draft and no invoice number') and the auth requirement ('Cotlet API key with access to this app'). It stops short of pagination or error behavior, but the additions are meaningful.

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-loads the resource and its payload, then adds draft semantics, usage, and auth in a compact block. The opening two sentences overlap somewhat ('all lines, amounts, payments and status' vs 'line items, tax rate per line, totals...'), which is minor redundancy but not bloat.

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 correctly describes what is returned, includes the draft-state edge case and the auth prerequisite, so an agent has enough to call it correctly. Only return formatting/pagination details are absent, which is a minor gap for a single-object fetch.

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 single parameter's description already points to list_invoices/create_invoice as sources, so the schema does the heavy lifting. The description adds no syntax or format detail beyond that, making the baseline 3 appropriate.

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+resource ('Get invoice') and immediately enumerates the returned content: line items, tax rate per line, totals and registered payments. An agent can distinguish it from bokio_list_invoices and bokio_create_invoice without opening any 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 concrete usage context: 'Use it right before recording a payment to check that nothing was paid already', which tells the agent precisely when this read is warranted. It does not name an explicit alternative or state when-not-to-use, keeping it just short of a 5.

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