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

Annotations already signal read-only, open-world, idempotent, and non-destructive behavior. The description adds context beyond annotations by stating 'Free, no credentials needed' and enumerating the data sources covered, which helps the agent understand availability and attribution requirements.

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, each earning its place: the first states purpose and output, the second covers cost and credentials, the third gives usage direction. Information is front-loaded and there is no redundancy.

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 zero-parameter listing tool, this is complete: it names the output fields, scope, access requirements, and when to invoke it. There is no output schema, but the description provides sufficient expectations for the return value.

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 declares zero parameters, so no parameter documentation is needed. The description compensates by detailing the output fields (id, name, data source, timezone, currency, licence, attribution), which is the relevant semantic content for this tool.

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?

Description states a specific verb ('List') and resource ('25 electricity grid zones GridHub covers') and names the exact fields returned. It clearly distinguishes from sibling get_* tools by scope: this is the enumeration of all zones, while siblings fetch data for specific zones.

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 guidance is given: 'Call this first if you are unsure which zone id to use.' It implies use before zone-specific tools like get_zone_brief or get_latest, though it does not explicitly name alternatives or state when not to use it.

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