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

Annotations already declare readOnlyHint and openWorldHint, so the safety profile is covered. The description adds no behavioral context beyond annotations—no mention of output shape, caching, or whether sections vary by locale/edition—but for a simple read-only lookup, nothing is contradicted and the bar is appropriately low.

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?

A single, front-loaded sentence with no filler. It states the resource and the sibling relationship immediately.

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 parameters and an output schema present, the description is nearly sufficient: it tells the agent that this returns section identifiers usable by metro_headlines. It could be slightly more explicit that the return value is a list of valid section slugs/names, but the output schema handles that detail.

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 tool takes zero parameters, so the baseline is 4. There are no parameter semantics to clarify, and the description does not need to compensate for schema gaps.

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 identifies the resource (Metro public editorial or RSS sections) and its relationship to a sibling (accepted by metro_headlines), which lets an agent infer this is a discovery/list tool for valid section values. It does not explicitly state the verb 'retrieve' or 'list', but the purpose is clear and differentiated from metro_article/news/headlines.

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?

Usage is implied: fetch this to learn which sections metro_headlines accepts. However, the description does not explicitly say when to call it, when to avoid it, or name alternatives (e.g., if sections can be omitted). The agent must infer the workflow from the word 'accepted by'.

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