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

Annotations only cover readOnly/openWorld, but the description adds the material operational facts an agent needs: a paid endpoint at $0.002 USDC per successful call via x402 on Base/Solana/Arc, and that failed calls are not charged. It also warns that the tool returns raw gauge readings rather than derived capacity, preventing misuse of the output.

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?

Four compact sentences, front-loaded with what the tool returns and in what units, then default, then the exclusion, then pricing. Nothing is repeated from the schema and no sentence is filler.

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?

An output schema exists, so return structure needn't be spelled out, and the description covers the remaining essentials: units, single-gauge scope, default station, source, what it does not compute, and the payment model.

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 station parameter is already documented, but the description adds semantics beyond the schema by explaining that KAUB is the default and characterizing it as a Middle Rhine barge bottleneck. That gives the agent a reason to keep or change the default, not just a syntax example.

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?

States a specific verb+resource pair (current water level W cm and discharge Q m3/s), names the source (PEGELONLINE/WSV), the scope (one German federal waterway gauge) and the default station. This is clearly distinguishable from siblings like logistics_mississippi_barge_rates or logistics_dardanelles_bosphorus.

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?

Gives the default station and explains why it matters (KAUB is a key Middle Rhine barge bottleneck), and explicitly excludes a nearby use case: 'Barging capacity is not calculated; this is gauge data only.' It does not name a specific alternative tool for capacity or price data, so it stops short of full when/when-not routing.

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