format_units

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

With no annotations provided, the description carries the burden of disclosure. It conveys the core conversion behavior but does not mention rounding/precision behavior, return type, or how the decimals parameter affects output beyond the schema. It is adequate for this simple pure function but lacks detail on edge cases.

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, front-loaded sentence that immediately states the action and includes a clarifying example. No wasted words, ideal for quick scanning.

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 fully described parameters and no output schema. The description clarifies the output as 'human-readable format,' implying a formatted string. Combined with the schema, this is sufficient for an agent to use the tool 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?

Schema coverage is 100%, so baseline is 3. The description's example (wei to ETH) aligns with the schema's value and decimals parameters but adds no new semantic information beyond what the schema already provides. The schema itself documents both parameters effectively.

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 clearly states the operation: converting a smallest unit value to a human-readable format, with a concrete example (wei to ETH). This distinguishes it from inverse tools like parse_units and leaves no ambiguity about the direction of conversion.

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 implies usage when you have a raw integer value and need a formatted decimal, but it does not explicitly mention alternative tools such as parse_units or provide when-not-to-use guidance. Given the sibling context includes parse_units, explicit differentiation would have been helpful.

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