Cheapest bus per day

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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, open-world), and the description adds genuinely non-structured behavior: each call fans out into one search per day (a latency/cost signal), prices are in Toman per adult, only buses with a free seat are counted, and days with no qualifying bus return no price rather than an error.

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?

Three short sentences, front-loaded with the output shape and then the routing rule. The only blemish is the mid-sentence parenthetical '(the site has no bus calendar)', which interrupts the main clause and could be folded into the following sentence without loss.

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, so the description must carry the return contract, and it does: per-day lowest price, per-day bus count, currency and unit (Toman per adult), the free-seat filter, and the empty-day representation. Nothing an agent needs to interpret a result or size its request 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?

Schema coverage is 100%, so all four parameters are already documented, making 3 the floor. The description still adds value by framing `days` as a cost dial ('keep `days` small') and by situating `date` as the anchor for the per-day walk, which the schema's 'starting at `date`' only partly conveys.

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 opens with a concrete verb and result shape: 'List the lowest bus price and the number of buses for each day from a start date.' It also names the exact sibling it competes with (al_buses) and states the condition that selects this one, so an agent can route without opening either 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?

Explicit routing guidance: 'Use before al_buses when the date is flexible' tells the agent both the alternative and the deciding condition (date flexibility). It adds a practical constraint — 'It runs one search per day, so keep `days` small' — that governs how to invoke it, not just whether to.

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