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

With no annotations, the description carries the full burden of explaining behavior, but it only says 'Expression discarded.' It does not state whether the tool returns a result, whether it mutates state, what side effects occur, or what happens to the nine accepted parameters. 'Discarded' is vague and unsupported by the schema.

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, but it is under-specified: 'Expression discarded' is cryptic and does not earn its place for a tool with nine parameters. Being brief is not helpful when the brevity hides the actual contract.

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 9 parameters, no annotations, and no output schema, the description is severely incomplete. It does not explain return values, errors, parameter selection, or any side effects, and it cannot be used to invoke the tool 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?

The schema provides descriptions for all 9 parameters, so the 100% coverage baseline applies. The description adds no parameter-level meaning and instead references an 'expression' that does not exist among the parameters, which slightly undermines trust but does not reduce what the schema already documents.

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 exposes nine unrelated string parameters (ref, url, city, feed, host, json, path, query) and contains no expression parameter. An agent therefore cannot tell what this tool actually does or how to invoke it for the stated purpose. The phrase 'Expression discarded' is ambiguous about whether a result is even returned.

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 when-to-use or when-not-to-use guidance and does not compare against sibling validators such as file-path-ok or validate-json. It only implies an arithmetic use case that the schema does not support, leaving an agent without actionable selection criteria.

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