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

Annotations already declare readOnlyHint=true and destructiveHint=false, so safety is covered. The description adds meaningful context beyond that: the exact returned content (lines, tax, balance, applied payments, email-open history) and the authentication requirement, which is not captured in 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 core purpose and well ordered, but the first two sentences overlap heavily: 'with lines, tax, payments applied and activity history' is restated as 'with every line, the tax, the balance due and the payments already applied.' A tighter version would merge them.

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 return-value burden and does so, listing the key fields and the email-activity detail. Combined with the auth note and the ordering advice, an agent has everything needed to call this 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 single invoice_number parameter is already documented as coming from list_invoices or create_invoice. The description adds no format or lookup guidance beyond that, so the baseline 3 for a fully-documented schema is correct.

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 (retrieve one sales invoice) and enumerates exactly what that includes: every line, tax, balance due, payments applied and activity history. The singular scope implicitly and effectively separates it from the sibling myob_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?

Gives an explicit workflow rule with a reason: read this before record_invoice_payment so a short payment is not mistaken for a full one. It also names a prerequisite (Cotlet API key with access to this app), so the agent knows both when to call it and what it needs.

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