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

Annotations already declare readOnlyHint=true, openWorldHint=false and destructiveHint=false, so safety is covered. The description adds genuinely new behavioral context: the data is nightly-sourced (implying freshness limits) and date-independent. A note on data staleness or caching would push this higher.

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 what the tool returns, then the sibling routing rule. Two sentences, no filler. The returned-field list is dense but every item is informative rather than padding.

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?

There is no output schema, yet the description enumerates the return fields so the agent knows what to expect. Combined with the date-independence note and the sibling handoff, nothing essential for correct invocation is missing.

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?

With 100% schema coverage and only two parameters already documented as English town names, the schema does the heavy lifting. The description implies the route is directional (from_town to to_town) and limited to Thai routes, but adds no format or matching guidance beyond that. Baseline 3 is appropriate.

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: the daily timetable of a Thai route from BestBus's nightly data, and enumerates exactly what comes back (departures/day, first/last bus, fare range, journey time, companies, boarding points, route page). That enumeration alone lets an agent distinguish it from search_buses without opening a schema.

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 names the alternative and the condition that selects it: 'No date needed; live seats on a specific date come from search_buses.' That is a clear when-not rule. It doesn't address the other sibling buses_from, so the routing picture is not fully complete.

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