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

Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=false, so the safety profile is covered elsewhere. The description adds only that the source is QuickBooks Online and the lookup is by Id; it says nothing about behavior on a missing/invalid Id or how the optional company argument is resolved when multiple companies are connected.

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?

A single front-loaded sentence with minimal waste. The trailing 'when no search or write answer already holds it' is slightly awkward phrasing but does carry routing intent rather than being pure filler.

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?

For a safe single-record read with annotations covering the safety profile and no output schema, the description is minimally adequate. It omits the one behavior an agent would want here – what happens if the Id is not found – and leaves the routing intent implicit.

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%, so both parameters are already fully documented in the schema. The description's 'by Id' merely restates the schema and adds no syntax, format, or fallback detail beyond it, 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 and resource ('Get a single invoice from QuickBooks Online by Id'), which is clearly distinct from the write siblings create_invoice/update_invoice/delete_invoice. It gestures at but does not name the read siblings (search_invoices, get_open_invoices) that an agent must distinguish it from, so it falls 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?

The clause 'when no search or write answer already holds it' implies usage context and hints that search_invoices is the alternative, but it never names the sibling nor states a concrete condition (e.g. 'use search_invoices to find an invoice when you don't have the Id'). Guidance is implied, not explicit.

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