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

The annotations only give a generic mutation profile (not read-only, not destructive, not idempotent), while the description discloses the actual side effects: credits are added to the customer's balance and a draft invoice is generated unless create_invoice is false. It also surfaces authorization scope, the workspace-claim gate with its 403 behavior, and the unlimited-bundle rejection rule — none of which appear in the structured fields.

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?

Three sentences, front-loaded with what happens to the balance and invoice before moving to constraints and prerequisites. Dense but each sentence carries distinct information; only the terse "Early access." fragment is slightly awkward.

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 three-parameter mutation with no output schema, the description covers effects, failure modes, and auth requirements thoroughly. It does not say what the call returns (grant or invoice identifier) or what happens on a repeat call, which matters somewhat given idempotentHint=false, but those are minor residual gaps.

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 create_invoice are documented in the schema, and the description only reinforces create_invoice's effect on invoice creation. plan_id has no description in either place, so the agent must infer that it references an existing bundle plan from context; the description doesn't compensate for that gap.

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 states a specific verb and resource — "Give a customer an active credit bundle" — and spells out the resulting effects (credits to balance, draft invoice for price). It is clearly distinct in meaning from create_credit_bundle_plan or update_credit_bundle_plan, but no sibling is named, so an agent must infer the distinction rather than being routed explicitly.

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?

It gives concrete preconditions and exclusions: early access, a Last Price credential with billing write scope required, a claimed workspace required with an explicit 403 failure mode for sandbox self-registration keys, and the rule that unlimited bundles cannot be granted. It stops short of naming alternatives such as top_up_balance or create_credit for cases where the grant is not appropriate.

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