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

Goes well beyond the annotations by disclosing the idempotency semantics in plain language ('safe to retry; an invoice is issued once'), the exact auth/scope requirement, an explicit failure mode (sandbox key from self-registration is refused with 403 until claimed), and an early-access caveat. That is the kind of operational context annotations cannot convey.

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?

Front-loaded with purpose and return value, then prerequisites and failure modes. Dense but every clause carries information; the only soft spot is the terse 'Early access.' fragment, which sits slightly awkwardly in the flow.

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 two-parameter mutation with no output schema, the description covers the outcome (hosted invoice URL), the email side effect, idempotency, auth scope, and the 403 onboarding trap. An agent has everything needed to call it correctly or diagnose a refusal.

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 100%, and the description's mention of `send` (emailing the customer) merely restates what the schema already says. No additional format, default, or edge-case detail for `invoice_id` is added beyond the schema's reference to list_invoices.

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 verb (issue), a specific resource (one of your invoices), and the mechanism/outcome (through your connected Stripe account, customer pays on Stripe's page, returns hosted invoice URL). This is clearly distinguishable from siblings like create_invoice, send_invoice, or get_invoice.

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?

Gives clear preconditions for use: needs a Last Price credential with billing write scope and a claimed workspace, and explains the `send` flag's effect. It does not explicitly route the agent away from near-siblings such as send_invoice or create_invoice, which keeps it short of a 5.

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