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

Annotations already declare readOnlyHint, openWorldHint, idempotentHint, and destructiveHint=false. The description adds useful behavioral context beyond that: the endpoint is keyless and is not reachable via query_dataset. It does not describe error behavior or response shape, but the annotation coverage lowers the burden and the added access constraints are valuable.

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 with no wasted words. The key facts are front-loaded: what the tool returns, the units, the source identifier, the cash-out context, and the access constraint that differentiates it from query_dataset.

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 simple two-parameter read-only tool with no output schema, the description is complete: it enumerates the returned fields, units, settlement-period granularity, source, and access model. The 48-row default behavior is covered in the input schema. Nothing critical 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?

Schema description coverage is 100%, so the schema already documents settlement_date and settlement_period with examples and the 1-48 range. The description adds output context (GBP/MWh, field names) but does not materially expand parameter semantics beyond what the schema provides. Baseline 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 clearly identifies the resource: Great Britain electricity imbalance prices for a settlement day, with specific fields (system buy/sell price, derivation code, reserve scarcity price, net imbalance volume) and units. It also distinguishes itself from query_dataset by naming the route constraint, so an agent can tell exactly what this tool offers.

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 explicitly explains when to use this tool: for Elexon system prices/cash-out prices. It also tells the agent why query_dataset cannot be used instead ('Elexon serves it outside the /datasets routes'), giving clear routing guidance among sibling tools.

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