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

Annotations already declare readOnly/destructive/openWorld, so the safety profile is covered. The description adds real value beyond them: it discloses the auth requirement ('Cotlet API key with access to this app') and that status comes from a fixed Procountor set. No rate limits or pagination notes, so not a 5.

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 resource and payload contents, then the usage cue and auth note. Four compact sentences with little waste, though the return-value enumeration is slightly verbose for a no-output-schema tool.

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 usefully enumerates what comes back (header, rows with quantity/unit price/VAT, totals, allocated payments). Combined with the auth note and status caveat, an agent has enough to call it correctly; minor gaps like error behavior remain.

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% with a single well-documented invoice_id parameter, so the schema already carries the semantics. The description adds nothing parameter-specific, which is the expected baseline when the schema does the heavy lifting.

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 ('Get sales invoice') and scopes it precisely as 'One sales invoice with rows, VAT, payments and status', which implicitly separates it from list_sales_invoices. It does not explicitly name sibling tools like list_sales_invoices or get_purchase_invoice, so it stops short of a 5.

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?

Explicitly tells the agent when to reach for it: 'Use it before approve_sales_invoice to read the totals.' That names a sibling and a sequencing condition. It gives no when-not guidance or alternatives for read-only inspection, so not a 5.

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