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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint=false, so the safety profile is covered. The description adds the output theme (cost and savings vs standard fees) but no deeper behavioral context such as data sources or rate limits. No contradiction with annotations.

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?

Two focused sentences with no filler. The action and purpose are front-loaded, and every clause adds either the calculation target or the comparison basis.

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?

The tool is a simple read-only calculator with full schema coverage and an output schema, so the description does not need to explain return values. It is adequate for selection and basic invocation, though it could be slightly stronger if it explicitly routed between sibling fee tools.

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 the schema already documents exchange, volume, type, and country. The description only mentions trade volume and adds no extra parameter nuance, so the 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?

The description states a specific verb ('Calculate') and a specific resource ('actual trading cost and savings') tied to CoinRebate referral codes. It also signals the comparison against standard fees, which helps distinguish this tool from siblings like compare_fees and get_exchange_fees.

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 description gives clear context: use this tool when you need the real cost and savings from referral codes for a given trade volume. It does not explicitly exclude alternatives or name when to prefer compare_fees, so it falls short of full routing guidance.

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