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

Annotations already declare readOnlyHint=true, destructiveHint=false, so the safety profile is covered; the description's genuinely additive line is that it does not reserve the number, which prevents a wrong assumption. It omits other behavior an agent would want: whether the value can change between calls, and the endpoint's auth/rate-limit characteristics despite openWorldHint=true.

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 plus the endpoint path, front-loaded with the returned value and followed immediately by the key caveat. Zero filler, nothing buried.

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?

There is no output schema, so the description must carry the return contract, and it only gestures at it ('the next free document number') without stating the response shape (string vs. object with number/number-set fields). For a trivial single-parameter read this is adequate but not complete.

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 enum values are documented in the schema, so the baseline is 3. The description contributes one useful constraint the schema lacks — only the *default* number set is consulted — but adds nothing about how 'custom' or the other enum values behave.

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 resource and scope: the next free document number from the *default* number set for a given document type. That distinguishes it from invbg_list_number_sets and the create_* tools, though it is a noun phrase rather than a verb and never names the sibling it supersedes.

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?

Usage is only implied — an agent must infer this is called ahead of invbg_create_invoice to preview a number. There is no explicit when-to-use/when-not-to-use guidance and no mention of what to do instead if a non-default number set is needed (list_number_sets is never referenced).

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