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

Annotations already declare read-only, idempotent, open-world lookup behavior, so the safety profile is covered. The description adds value beyond that by disclosing the shape of the answer (lines, transfer location, direction, stop count, fare) and by imposing a grounding constraint ('answer only from this tool's results'), which is real behavioral context for an agent composing a reply.

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?

Front-loaded with the purpose and return contents, followed by a compact Args block and a short grounding caveat. Every sentence serves a distinct function and there is no restatement of the tool name or annotations.

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?

With no output schema, the description correctly covers the return contents, and it also states the accepted input formats, which the schema does not. The remaining gap is error/ambiguity behavior — what an agent should do if a station name does not resolve — but for a simple two-argument lookup this is close to complete.

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 0% — the input schema gives only bare string titles — so the description must carry the load, and it does: each argument accepts a station name, a station code like 'C10', or an airport name/code such as 'DCA' or 'Dulles'. It stops short of covering case sensitivity, spacing, or what happens with an invalid or ambiguous station.

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 specific verb and resource ('How to ride Metrorail between two stations') and enumerates exactly what the answer contains: line(s), transfer point, direction, stop count, and fare. That distinguishes it from generic siblings like get_route or plan_trip by scoping it to rail-only trips, though it never names those siblings explicitly.

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?

'Use this for EVERY Metrorail trip — never assume two stations share a line' gives a clear positive trigger and a caution against shortcutting. It lacks explicit when-not guidance and does not name which sibling to use instead for bus trips, multi-modal planning, or fare-only questions.

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