One line

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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false and openWorldHint=false, so the safety profile is covered. The description adds genuinely useful behavioral context beyond that: exactly which metric families and time windows are computed and that reasons/causes are TfL-sourced. It stops short of mentioning cost, latency, or data freshness.

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?

It is a single dense sentence, but the scope ('One line in depth') is front-loaded and every clause enumerates a distinct return category rather than padding. Slightly run-on, but no sentence is wasted.

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 and only one parameter, the description carries the burden of explaining what comes back, and it does so across all the metric groups and time windows. It does not describe response shape or ordering, which is a minor residual gap for an agent parsing the result.

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?

There is a single required parameter with 100% schema description coverage; the schema already states it is a line id from list_lines with concrete examples. The description adds nothing about the line argument, so the baseline 3 applies.

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 uses a specific verb ('One line in depth') and enumerates the exact resource scope: open disruptions, 24h/7/30/90-day disruption metrics, latest disruptions with TfL reasons and causes, and hour-of-day onset patterns. It is clearly differentiated from list_lines by being per-line and 'in depth,' though it never names the sibling tools it supersedes.

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 'in depth' framing implies this is the detailed per-line drill-down versus the aggregate siblings (current_status, period_stats), but no explicit when-to-use or when-not guidance is given. An agent must infer that it should reach for this tool after list_lines resolves a line id, which is only hinted at via the schema's reference to list_lines.

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