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

Annotations already declare readOnlyHint=false and destructiveHint=true, so the safety profile is covered by structured data. The description's 'amount, margin, VAT, or carrier cost' phrasing hints at a partial/selective update rather than full replacement, which is useful, but it never resolves the critical ambiguity that every optional field defaults to null — whether omitting a field leaves it unchanged or clears it is unstated for a destructive write.

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?

A single sentence with no filler, and the verb plus resource lead immediately. It is efficient, though so compact that it carries no supporting context about update semantics.

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 destructive 7-parameter mutation with no output schema, the description omits partial-vs-full update semantics, null handling, and any permission or reversibility note, and gives no guidance for distinguishing it from UpdatePartnerRate. The schema happens to be fully documented, but the behavioral contract an agent needs before writing 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 description coverage is 100%, so each of the 7 parameters is already documented, and the baseline for that case is 3. The description restates four of the fields (amount, margin, VAT, carrier cost) and omits useInPreInvoicing and intentId without adding any semantics the schema does not already carry.

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?

The description pairs a specific verb ('Update') with a specific resource ('existing partner surcharge') and names the mutable fields (amount, margin, VAT, carrier cost), so the action is unambiguous. It does not, however, distinguish this tool from closely named siblings like UpdatePartnerRate, UpdateCustomRate, or AddPartnerSurcharge.

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?

'On an existing partner surcharge' weakly implies the record must already exist and a surchargeId is required, but there is no explicit when-to-use, no when-not-to-use, and no routing to UpdatePartnerRate or UpdateCustomRate, which sit in the same sibling cluster. The agent must infer tool selection purely from the name.

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