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

Annotations only include the title, so the description carries the burden of behavioral disclosure. It adds useful content context (feed sizes, expired-feeds detection) but does not explicitly state that this is a read-only operation, nor does it mention any side effects, auth requirements, or output format. This is typical for a list tool, but not fully transparent.

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?

The first sentence is an indirect 'Which...' clause rather than a crisp verb-first statement, making it heavier than needed. The second sentence is a fragment. The content is meaningful but the phrasing is awkward and not front-loaded, detracting from efficient comprehension.

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?

For a simple tool with one optional parameter and no output schema, the description covers the main purpose and includes notable details (sizes, expired feeds). However, the phrase 'look right but whose timetables have run out' is vague, and the return structure is only partially hinted at (size), leaving some uncertainty about the full response.

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?

The schema already provides a complete description for the only parameter ('country'), so the description adds no additional parameter details. Since schema coverage is 100%, the baseline of 3 applies; the description does not conflict or enhance the parameter meaning.

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 clearly identifies the resource (published timetables/transit feeds) and the core action (listing which are carried and which could be added), with an explicit mention of feed sizes. It distinguishes itself from transit_arrivals, transit_nearby, and transit_status by focusing on the feed catalog, but lacks a direct imperative verb like 'list' or 'retrieve'.

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?

It provides a clear use case: 'so an operator can see what switching one on costs' and adds the nuance of expired timetables. However, it does not explicitly state when to use this tool over alternative transit tools or when not to use it, so it falls short of explicit when/when-not guidance.

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