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

With no annotations, the description must disclose behavioral traits. It does state the tool 'Shows exactly how much you earn' and gives an output example, which is behaviorally transparent. However, it does not explicitly state that this is a read-only operation or mention any side effects, which would be valuable given the lack of 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?

The description is two sentences long, front-loaded with the main function, and includes a helpful example. Every word earns its place with no filler or redundancy.

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 simple with 3 params and no output schema, and the description plus schema cover the main functionality. The example clarifies the output format. It could mention edge cases like what happens when no brands match, but overall it's sufficient for an agent to select and invoke correctly.

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?

The schema already describes all 3 parameters with 100% coverage, including that brandIds can be omitted to use category auto-discovery. The description adds marginal value by reinforcing the purchase amount context but doesn't offer new parameter semantics beyond the schema. Baseline of 3 is appropriate.

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 uses the specific verb 'Compare' and resource 'cashback rates across brands' for a specific purchase amount. It provides a concrete example ('Buy $100 at Nike = $8 back vs Adidas = $3 back') that clearly distinguishes it from siblings like compare_brands, which likely compare other metrics. This is a clear, specific purpose.

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 explicitly positions this as 'The key decision tool for purchase routing,' implying when to use it for purchase decisions. It does not explicitly mention alternatives or exclusions, but the use case is clear from the example. The phrase 'for a specific purchase amount' narrows the context.

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