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

Goes well beyond the annotations (destructive/non-idempotent) by disclosing credit payment, print release, the cancellation window, what happens on insufficient credit (payment link returned, assistant cannot pay), and the account prerequisite. This is exactly the extra context annotations cannot carry.

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 the trigger condition and the credit/cancellation consequences; each sentence carries distinct information. It is dense rather than padded, though the terms/withdrawal aside is longer than strictly necessary.

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 still explains the return behavior (payment link on low credit), the legal gate, and the account requirement, covering everything needed to invoke 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 67%; confirm and user_accepted_terms are documented in the schema, but letter_id has no description anywhere. The description reinforces what 'confirmed' entails ('recipient, content and total price') and ties user_accepted_terms to the Terms and withdrawal waiver, adding meaning beyond the schema.

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 ('printed and posted' letter) with explicit scope ('Posts paper letters only: no email, fax or parcels'). It also names the sibling it interacts with (cancel_letter), so an agent can separate it from compose_letter/create_letter without opening schemas.

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 explicit preconditions: only call after the user confirmed a specific draft AND accepted Terms and immediate printing. Names the alternative path (cancel_letter, valid only until production starts), leaving nothing to inference.

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