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

Annotations already establish read-only, open-world, idempotent, and non-destructive behavior. The description adds useful behavioral context beyond annotations: half-hour timestamps, forecast vs actual intensity, qualitative index, update cadence, and the meaning of lower values. There is no contradiction with the 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 front-loaded with the action and resource, then provides return fields, update frequency, interpretation guidance, use cases, and licensing/cost note. Every sentence contributes meaningful operational or selection-relevant information without repetition or padding.

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?

Given the output schema, rich annotations, and fully documented optional parameter, nothing critical is missing. The description covers the scope, return contents, refresh behavior, qualitative meaning, and even cost/licensing, making it complete for an agent deciding whether and how to call this tool.

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?

There is only one optional parameter, 'locale', and the schema fully documents it as reserved for future use and instructs to omit it for the standard response. The description does not add parameter-level detail, but because schema coverage is 100%, the baseline of 3 is appropriate.

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 names a specific verb and resource: 'Get the current national carbon intensity of UK electricity generation' from the National Grid ESO. It is clear and specific, but it does not explicitly differentiate this from the sibling tools carbonintensity.energy.forecast, generation, or regional, relying instead on the word 'current' and 'national' to imply the distinction.

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 application context: smart energy scheduling, EV charging optimisation, and sustainability dashboards, plus the 30-minute update cadence. However, it does not explicitly state when to prefer this tool over its forecast/generation/regional siblings or 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.