List zones

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

Annotations already cover safety (readOnlyHint, idempotentHint, non-destructive), so the description's added value is the auth/access disclosure: 'Free, no credentials needed.' It also reveals the fixed and finite nature of the result set ('25 zones'), which is behavioral context beyond the structured annotations. No contradiction with annotations.

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 sentences, each earning its place: the first delivers the core function and output contract, the second the access requirement, the third the usage routing. Information is front-loaded and there is zero filler.

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, the description must explain return values — and it does, enumerating the exact fields an agent will receive (id, name, data source, timezone, currency, licence, attribution). Combined with annotations covering the safety profile and zero parameters, nothing an agent needs to call this tool correctly is missing.

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 has zero parameters, so the baseline of 4 applies and the description carries no parameter documentation burden. The 'no credentials needed' statement further clarifies that no hidden inputs are required, which reinforces the empty-schema signal.

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 ('List'), a resource ('electricity grid zones'), and a concrete scope ('the 25 ... zones GridHub covers'), then enumerates the returned fields (id, name, data source, timezone, currency, licence, attribution). The enumeration of returned fields clearly differentiates it from siblings like get_zone_brief and get_history, which operate on a specific zone or dataset.

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?

Provides explicit when-to-use guidance: 'Call this first if you are unsure which zone id to use.' This tells the agent this is the discovery/enumeration tool and the natural entry point before zone-specific siblings. It doesn't name specific alternatives or exclusions, but the routing signal is clear and actionable.

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