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

Goes well beyond the annotations: draft=false is irreversible ('can no longer be edited'), 'a final invoice is a legal document', the call fails on bad totals or unaccepted VAT rates, default ledger mapping applies when omitted, and it requires the user's API key with confirm-before-call. This is exactly the mutation/legal/permission context annotations alone 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 the draft default before drilling into edge cases and confirmation rules. It runs long, but nearly every sentence carries a distinct behavioral fact; only the final confirmation/API-key sentences are somewhat boilerplate.

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?

With no output schema, the description compensates by naming the return values (invoice_id and amounts). For a 6-parameter mutation tool it covers mutability, idempotency, validation failures, defaults, and auth/confirmation needs, so an agent has everything required to call it correctly.

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%, so the baseline is 3; the description adds real meaning on top by explaining that amounts are strings, that missing ledger accounts fall back to the company default mapping, and why external_reference exists (dedupe on repeat runs). Useful elaboration beyond the schema text.

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+resource (create a customer invoice) and immediately scopes it with the default draft behavior. An agent can distinguish it from pennylane_finalize_customer_invoice and pennylane_send_customer_invoice without opening any schema.

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?

Clearly explains when to use draft=true vs draft=false, when to set external_reference for idempotency, and the confirm-before-each-call requirement. It does not explicitly name a sibling (e.g. finalize_customer_invoice) as the alternative path, so routing is implied rather than explicit.

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