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

Goes beyond the annotations by explaining the concrete consequence of non-idempotency ('calling twice creates two products'), naming required scopes (READ:PRODUCT / WRITE:PRODUCT), and disclosing a merchant-configuration validation rule for vat_percentage. The endpoint is included; only side effects on inventory or error modes are left unaddressed.

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?

Roughly five terse clauses, each carrying distinct load (mutation type, destination, idempotency, auth, validation constraint, price units, route), with the most decision-relevant facts front-loaded.

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 4-parameter create tool with no output schema and no annotations on auth, the description covers safety, idempotency, permissions, and validation adequately. The one gap is not saying what the successful response yields (e.g., the new product's id), which an agent must know to chain follow-up calls.

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%, so field-level meaning is already carried by the schema. The description reinforces the VAT-rate constraint and smallest-currency-unit prices, but adds no information about the nested variants structure beyond what the schema documents, so baseline 3 applies.

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 ('add a new product to the Zettle product library') and clarifies the downstream effect (appears in POS and online store). This clearly separates it from the read-only siblings like zettle_get_product and zettle_list_products.

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?

The 'WRITE:' prefix plus the creation framing make the when-to-use condition evident, and the non-idempotent warning steers against blind retries. It stops short of explicitly naming the sibling read tools as alternatives, but the create-vs-fetch distinction is unambiguous.

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