All zones right now

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

Beyond the readOnly and idempotent annotations, the description discloses meaningful behavioral traits: data is 'Rebuilt every ight minutes,' authentication requirements are spelled out, and free sample mode truncation is explained. It also notes that sample results are clearly marked, which is valuable for an agent interpreting output. This significantly exceeds what annotations alone provide.

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 core purpose and examples are front-loaded in the first sentence, with freshness and auth details following in a logical order. The auth section is somewhat lengthy, but each detail serves the agent's ability to call the tool correctly. It is organized and not padded, though slightly dense.

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 tool with one optional parameter and no required inputs, the description covers purpose, freshness, authentication, and sample-mode behavior. Because there is no output schema, 'headline values' is a bit vague about exact returned fields, but the examples hint at price and demand. Overall, an agent has enough context to select and invoke the tool 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?

Schema coverage is 100%, so the baseline is 3, but the description adds meaning by explaining when to use the api_key argument versus the Authorization header and what happens without credentials. This gives an agent practical guidance beyond the schema field description.

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 states a specific verb and resource: 'Current headline values for all 25 zones in one call.' It also gives concrete use examples ('which European zone has the lowest price right now') that make the tool's purpose unmistakable. This clearly distinguishes it from per-zone or historical sibling tools like get_zone_brief and get_history.

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?

The description provides clear context for when to use the tool: comparing zones, checking prices, and ranking demand. It calls itself 'the cheapest way to compare zones,' which strongly implies the intended use case. It does not explicitly name sibling alternatives or state when not to use it, so it stops short of a 5.

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