expr

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

Annotations provide readOnlyHint=true, and the description reinforces this with 'Read-only, no side effects' and adds context about safe AST subset. There is no contradiction; description adds value beyond 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 concise (7 short sentences) and front-loaded with the core purpose. Each sentence adds unique information: purpose, safety, operations, return format, usage context, and alternatives. No wasted words.

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 the simplicity of the tool (3 parameters, no output schema), the description covers: input (tokens), operations supported, return format (JSON), usage guidelines, and alternatives. It is complete for an agent to use 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% (baseline 3). The description adds value by listing supported operations (+, -, *, /, %, comparisons, regex, string ops) which gives semantic context to the 'tokens' parameter beyond the schema example. This justifies a 4.

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 it evaluates arithmetic and string expressions in a safe AST subset, lists supported operations, and explicitly distinguishes from sibling tools 'test' and 'factor' by stating it is not for file-based predicate tests.

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 explicit guidance: 'Use for calculations and conditional logic in agent workflows. Not for file-based predicate tests — use 'test' or '[' for path checks. See also 'test', 'factor'.' This tells when to use and when not to use, with alternatives.

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