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

With no annotations, the description must carry behavioral disclosure, but it only says 'Expression discarded' and never states what is returned or what side effects occur. That single trait is also misleading because the schema contains no expression parameter to discard.

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 with the main verb phrase, with no filler. But it is under-specified rather than appropriately concise, and the dangling second sentence adds confusion instead of clarifying behavior.

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?

A nine-parameter tool with no annotations and no output schema needs a far richer definition. The two-sentence description does not say which input drives the operation, what result the caller can expect, or how to invoke it, so an agent cannot correctly call it.

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 parameter coverage is 100% and the parameter descriptions are individually clear, so the baseline is not zero. However, the description adds no mapping from its promised 'expression' to any schema field, making the schema descriptions irrelevant to the advertised purpose.

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 phrase 'Evaluate a+b style arithmetic' names a specific operation, but it is contradicted by the schema: none of the nine parameters (ref, url, city, feed, host, json, path, query) is an arithmetic expression. 'Expression discarded' further muddies whether a result is returned or only validated, and no sibling differentiation is offered.

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 no explicit when-to-use guidance, exclusions, or alternatives. The only implicit signal is 'a+b style arithmetic', which is unusable because no matching input exists in the schema.

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