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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint=false, but the description adds useful behavioral context: it never raises a protocol error, returns an error object instead, and is safe to retry after correcting input. It also clarifies that the calculation includes percentage fees, which explains why the result is not simply cost divided by one minus margin.

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?

The description is front-loaded with the core purpose and then adds only relevant details: an example, sibling routing, error behavior, and retry safety. It is somewhat dense, but most sentences earn their place for a calculation tool with fee and margin 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?

Given that an output schema exists and all parameters are fully documented, the description is complete enough to call the tool correctly. It also covers the important non-schema behavior around errors and retry safety.

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 all six parameters are already documented in the schema. The description provides a typical input and output example, but it does not add meaning beyond the schema for parameters such as charm_ending, payment_fee_pct, or payment_fee_fixed.

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 states a specific action and outcome: working backwards from desired margin to the price to charge, including processor fees. It explicitly distinguishes itself from margin_check, so an agent can select it 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?

It gives explicit usage guidance: use when setting a price list, and not for checking an existing single price because that is margin_check. This is a clear when-to-use and when-not-to-use instruction with a named alternative.

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