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

Annotations already cover the safety profile (readOnlyHint, idempotentHint, destructiveHint=false), so the bar is lower — and the description still adds genuinely new context by disclosing the RBAC restriction and the exact failure signal ('only the owner and billing contacts may read it (`403 rbac.insufficient_level`)'). It does not discuss rate limits or pagination, but for a single-object read those are minor.

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 tight sentences, zero filler: the return contents come first and the permission/error note second. Every clause carries information an agent can act on.

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?

An output schema exists, so return-shape documentation is not required, and the description nevertheless enumerates the key fields. Combined with the RBAC note and the read-only annotations, an agent has everything needed to call this correctly; only the tenant_id default behavior is left 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 0% for two parameters, so the description must carry the load and does not. It never explains what 'authorization' expects or how 'tenant_id' behaves (empty default, whether it falls back to the caller's tenant) — the phrase 'the tenant's stored billing details' only loosely implies tenant scoping.

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?

The description gives a specific verb and resource ('Return the tenant's stored billing details') and enumerates the exact fields returned (VAT id, invoice address, invoice email, PO reference). It implicitly separates itself from the sibling 'complete_billing' by framing itself as a completeness check, though it never names that sibling outright.

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?

'Call this to check whether billing is complete' states a clear use context rather than just describing the resource. It stops short of an explicit when-not-to-use or an alternative-tool pointer, so it is clear but not exhaustive.

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