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

Beyond the readOnly/openWorld annotations, it discloses the required READ:PURCHASE scope, the underlying endpoint GET /purchase/v2/{purchaseUuid}, and that a deprecated ID form will be rejected. That is exactly the extra context an agent needs before calling.

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?

One dense front-loaded sentence plus an auth clause and endpoint suffix; every element earns its place. The nested parenthetical is long but carries the critical deprecation warning, so it isn't waste.

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 one-parameter read tool with no output schema, the description covers input provenance, auth requirement, endpoint, and the shape of the returned data. Nothing needed to call it correctly is missing.

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 already 100%, so the baseline is 3, but the description adds semantic value by disambiguating purchaseUUID1 from the deprecated short purchaseUUID. It reinforces the format without repeating the UUID example already in 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 and resource: fetch one purchase (sale or refund) in full by purchase UUID, listing the payload contents (line items, VAT, payments, refund links). It is clearly distinguishable from zettle_list_purchases, which it names as the source of the identifier.

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 explicitly routes the agent: get the ID from zettle_list_purchases' purchaseUUID1 field, and it warns that the older short purchaseUUID is deprecated and rejected. It doesn't state when-not-to-use beyond that, but the single-purchase vs list split is unambiguous.

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