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. The description adds only that it fetches one record by Id from QuickBooks Online; it says nothing about not-found behavior or what is returned, and there is no output schema to fill that gap.

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 no repetition or filler. The trailing conditional is slightly opaque, which keeps it short of a 5, but every clause carries intent.

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 two-parameter read-only retrieve, the definition plus annotations plus a fully-described schema cover what an agent needs to call it. The absence of any return-shape note is the only gap, and it is minor for a single-record getter.

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 both parameters (id, company) are documented in the schema itself. The description only echoes 'by Id' and adds no format, default, or multi-company resolution detail beyond what the schema states. Baseline 3 applies.

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?

Names a specific verb and resource ('Get a single purchase from QuickBooks Online by Id'), which distinguishes it from search_purchases and list_purchases_without_payee by scope. It never names a sibling explicitly, so the differentiation is inferred rather than stated.

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 trailing clause 'when no search or write answer already holds it' gestures at when to use it, but it is cryptic — it doesn't name search_purchases or explain the condition concretely. Enough to imply fallback usage, not enough to route an agent confidently.

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