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

Annotations already declare readOnly, idempotent, non-destructive and openWorld behavior, so the safety profile is covered. The description adds value the annotations do not: 'Free, no credentials needed,' which tells the agent no auth setup is required before calling. It stops short of noting rate limits or response size, but for a 25-item static catalog that is a minor gap.

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?

Two tightly packed sentences with the core payload list front-loaded and the routing advice last. Every clause carries information (coverage count, fields, sources, cost/auth, invocation order) with no 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?

An output schema exists, so return values need not be explained, yet the description still summarizes them helpfully for routing. With no parameters, no credentials, and full annotation coverage, an agent has everything needed to call this correctly.

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, and the schema accepts no properties, so there is nothing for the description to disambiguate. Baseline 4 applies; the description's field enumeration describes the response rather than inputs.

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 and resource ('List the 25 electricity grid zones') and enumerates exactly what each entry contains (id, name, data source, timezone, currency, licence, attribution). An agent can distinguish this catalog-lookup tool from get_zone_brief or get_latest without opening any schema.

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?

Explicitly prescribes a trigger condition: 'Call this first if you are unsure which zone id to use.' That is clear when-to-use guidance, though it does not name the specific sibling tools (get_zone_brief, get_latest, get_history) that consume a zone id, nor state any when-not condition.

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