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

Goes beyond the annotations (readOnlyHint, idempotentHint, openWorldHint) by disclosing the commercial/rate-limit behavior: a few free samples per day, then $0.001 USDC per call via x402. That is genuinely useful context an agent needs before calling, though the return-shape behavior is left to the output 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?

Two sentences, zero waste. The functional purpose is front-loaded and the cost/model detail follows. Nothing extraneous.

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 values need no explanation, and the description supplies the missing mode vocabulary and cost model. The only gap is the lack of explicit routing versus the tube-status/line-status siblings.

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% but the schema description is only the generic label 'Mode' with no enum. The description compensates by enumerating the valid values (tube, overground, elizabeth-line, dlr, tram, bus), which the schema does not provide — real added value beyond the structured field.

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 clear verb+resource: 'Live status of every line for a mode.' The scope ('every line for a mode') implicitly differentiates it from the single-line line-status and tube-only tube-status siblings, but the differentiation is left to inference rather than stated outright.

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 mode enumeration hints at when this tool applies, but there is no explicit guidance on when to pick this over london-transport__tube-status or london-transport__line-status. Usage is implied by the scope rather than stated.

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