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

With no annotations, the description must carry the full behavioral disclosure burden. It only states that the expression is 'discarded,' which is vague and does not explain side effects, output behavior, permissions, or the fact that none of the nine schema fields can actually hold the expression. This is insufficient for an apparently action-performing tool.

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 short and front-loaded, with the main operation stated first and no filler. The second sentence is terse to the point of ambiguity, but as a conciseness measure it is efficient.

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 nine-parameter tool with no annotations and no output schema, this description is far from complete. It does not explain return values, how any input relates to the arithmetic operation, error behavior, or whether the tool is state-changing, so an agent cannot reliably invoke 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?

Although schema coverage is 100%, the description introduces an 'expression' concept that has no corresponding property among ref, url, city, feed, host, json, path, or query. It does not add meaning to the existing parameters; it actively misleads an agent about which field should be populated.

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 names a concrete operation: 'Evaluate a+b style arithmetic.' This is a specific verb and resource, and no sibling tool covers arithmetic evaluation. However, the follow-up 'Expression discarded' is ambiguous and no schema parameter corresponds to an expression, so the stated purpose is not cleanly actionable.

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?

There is no guidance on when to use this tool versus alternatives, what conditions select it, or what prerequisites exist. The phrase 'Evaluate a+b style arithmetic' only implies a narrow arithmetic use case but gives no exclusions or comparisons to sibling tools.

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