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

Annotations already declare readOnly, idempotent, non-destructive, open-world, so the safety profile is covered. The description adds genuinely useful behavioral context: departures are planned main-terminal times, not live intermediate-stop ETAs, and limit applies only to that action. That is real value beyond the annotations, but return shape and freshness/staleness of schedule data are left unaddressed.

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, front-loaded sentences with no filler; the primary capability comes first and the caveats follow. The telegraphic phrasing ('limit applies only to departures') is terse but unambiguous.

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 not be described, and the annotations cover the safety profile. Given three simple parameters, the remaining need is guidance on line_code format and the info-versus-departures distinction, which is the only real gap.

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 description coverage is 0%, so the description carries the burden. It does map loosely onto the three enum actions via 'info, ordered stops, planned departures' and clarifies that limit applies only to departures. However, line_code format and units/bounds for limit are never explained, so the compensation is partial.

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 (Get) and resource (IETT line), and enumerates the three modes of content: info, ordered stops, planned departures. It does not distinguish itself from the close sibling istanbul_next_departures, which also covers departures, so an agent must infer the split from the 'planned main-terminal' vs 'live intermediate-stop' phrasing.

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 one explicit exclusion ('not live intermediate-stop ETA') and one explicit routing rule (cross-operator notices go to istanbul_transport_disruptions). It also scopes the limit parameter to departures only. It stops short of saying when to pick action=info versus stops versus departures, leaving that to the enum.

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