Latest values for a zone

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

Beyond annotations (readOnly, idempotent, non-destructive), it reveals meaningful behavior: some European day-ahead timestamps can be ~36h in the future, outputs include unit/timestamp, and free sample mode truncates data while marking results. 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?

The description is dense but every sentence earns its place: scope, example use, caveat, alternative tool, authentication, and fallback behavior. It is front-loaded with the core semantics before auth details.

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 read-only lookup with no output schema, the description covers data scope, timestamps, units, sibling routing, auth modes, and sample-mode behavior. An agent has enough context to call get_latest correctly without additional documentation.

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 already covers both parameters fully, including zone enums and api_key guidance, so baseline is 3. The description adds value by explaining how the api_key parameter relates to the preferred Authorization header and what happens without credentials (sample mode, truncation).

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 names a specific verb/resource: returns the most recent value of every metric a zone publishes, with concrete examples (price, demand, generation by fuel, carbon intensity). It also differentiates from get_zone_brief by noting it can return day-ahead prices up to ~36h in the future.

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 states this is the right tool for 'what is the price/demand/carbon intensity in X right now' and tells the agent to use get_zone_brief when a strictly at-or-before-now value with historical context is needed. It also documents authentication requirements and the no-credential fallback mode.

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