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

Beyond the readOnly/idempotent annotations, the description discloses the critical behavior that this build returns no record, which saves the agent from wasted calls and misinterpreted empty results. It does not explain error shape or whether the call succeeds silently versus failing.

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?

Two short sentences, front-loaded with what the tool does and immediately followed by the constraint. Every clause carries information; nothing is redundant.

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 single-parameter stub with no output schema, the description covers the essentials: what it would return and why it currently returns nothing. It falls short only in not routing the agent to a working alternative.

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 invoiceId property already documents that it is "Ignored until phase 2." The description adds no further meaning about the parameter, so the 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?

"Returns one invoice" gives a specific verb and resource, which contrasts implicitly with the sibling list_invoices. It does not name that sibling or state the single-record scope explicitly, so differentiation is left to inference.

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 description does state a clear exclusion ("Not available until phase 2"), which effectively tells the agent not to rely on this tool. However, it never points to the alternative (list_invoices) or explains how to obtain invoice data in the current build.

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