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

The annotations already establish that this is a read-only, idempotent, non-destructive operation. The description adds meaningful behavioral details: the null result when all characters repeat and the one-credit cost.

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 short, front-loaded sentences plus a cost note. Every element contributes directly to understanding the operation and its result.

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 simple one-parameter pure function, the description covers the core operation and the important all-characters-repeat outcome. Minor edge cases such as empty-string behavior or character encoding are not addressed, but no output schema is expected to compensate.

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?

There is only one parameter and the schema fully describes it as the input string to search. The description does not add constraints such as case sensitivity, whitespace handling, or Unicode behavior, so it matches the baseline for complete schema coverage.

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 precise verb and resource: finds the first character in a string appearing only once. It also defines the negative result, so the tool is immediately distinguishable from neighboring algorithm utilities.

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?

Usage is implied clearly by the task itself, and the null-return edge case adds useful context. However, the description does not explicitly say when to choose this tool over alternatives or mention related tools.

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