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 structurally. The description adds only the default source and the invoice exclusion; it does not mention staleness of ledger data, latency of a live sweep, or permission requirements. With annotations carrying most of the burden, a 3 is appropriate.

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 fragments, front-loaded with the scope and default, with zero filler. It is efficient, though the terseness borders on under-specification rather than true conciseness.

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?

The tool is a simple read with an output schema, so return-value explanation is not required. Still missing is any note on ledger staleness vs. live freshness trade-off and on the undocumented connection_context parameter, which leaves the agent with a small gap before calling.

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 67%: customer_id and source are documented in-schema, including the ledger/live enum semantics, while connection_context is undocumented in both places. The description only reinforces the ledger default already stated in the schema, adding no format or constraint detail. Baseline 3 fits given the schema does the heavy lifting.

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 the resource ('billing setup') and the scope ('for one customer'), and the name supplies the verb (get). The addition of 'No invoice retrieval' narrows expectations, though no sibling tool is named to contrast with. An agent can tell what it returns without opening the schema, but the phrasing is a fragment rather than a stated action.

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?

'(ledger by default)' communicates the default read path and 'No invoice retrieval' sets a boundary, which is usage-relevant. However, there is no explicit when-to-use vs. when-to-use-another-tool guidance; the agent must infer that this is the read-side counterpart to billing/budget mutation tools.

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