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

Annotations already declare readOnlyHint and idempotentHint, so safety is covered. The description adds behavioral context: it computes live from the venue's per-gauge data, uses a specific measurement ratio, and compares advertised vs actual. This goes beyond the annotations and helps an agent anticipate the tool's computational nature. No contradiction with 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 packs a lot of information into two sentences with no filler. The purpose is front-loaded ('Call this before repeating...'), followed by a detailed explanation of the computation. The structure is efficient, though the long second sentence could be slightly more readable, but it earns its length.

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 tool with no parameters and an output schema present, the description adequately explains what it does and why. It contextualizes the output (comparison, structural ceiling explanation) without needing to describe the return format, which is left to the output schema. The only minor gap is that it doesn't explicitly state the output is a report, but that is inferable.

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 tool has zero parameters, so the schema is trivially 100% covered. The description explains what data the tool uses internally (venue's per-gauge data, fees, bribes, vote fraction) without needing to document input parameters. This is appropriate for a no-arg tool.

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?

Description clearly states the tool's function: comparing Hydrex's advertised weekly projection against actual collected income, and explaining the structural ceiling via per-gauge data. It uses a specific verb ('Call'), resource ('Hydrex'), and includes a distinguishing detail ('measured at 0.089% of the projection'). This sets it apart from sibling tools like hydrex_position or hydrex_vault that likely report raw position data.

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?

Explicitly instructs when to use: 'Call this before repeating any Hydrex APR or yield projection.' This is a direct usage condition. It also highlights that it is free, keyless, and read-only, which encourages adoption and clarifies no setup is needed. Does not need to mention alternatives since it is clearly the go-to for verification.

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