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

With no annotations, the description carries the full burden of behavioral disclosure, but it only says 'Expression discarded,' which is confusing because no expression parameter exists. It does not explain what is returned, whether side effects occur, how other parameters are handled, or what happens on invalid input.

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 text is short and front-loaded, so it earns some credit for conciseness. However, it is under-specified for a tool with nine parameters and a non-obvious purpose; the second sentence references a nonexistent input and therefore does not earn its place.

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 description is severely incomplete for a tool with this schema complexity and sibling context. It fails to state how the expression is provided, what the output is, when to prefer this tool over siblings like validate-json, normalize-url, weather-hint, or file-path-ok, and what behavioral guarantees exist.

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 the baseline is 3, but the description adds no useful parameter semantics and actually introduces an 'expression' concept absent from the schema. The nine documented parameters have clear individual descriptions, yet none of them is connected to 'a+b style arithmetic,' leaving the agent unable to construct a correct invocation.

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 claims the tool evaluates 'a+b style arithmetic', but the input schema contains nine unrelated optional parameters (ref, url, city, feed, host, json, path, zone, query) with no way to supply an arithmetic expression. This is misleading rather than clarifying: an agent cannot determine what resource is actually operated on or how the advertised purpose maps to the schema.

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?

No guidance is provided about when to use this tool versus any sibling tool. Given the abundance of similar validation/shape-checking sibling tools, the description offers no exclusions, alternatives, or context to help an agent select this tool correctly.

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