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

Annotations already cover read-only, idempotent, and non-destructive hints. The description adds valuable behavioral context beyond that: 'Keyless' (no authentication), the finite scope 'all 84', and what each entry contains (code, holdings, window parameters). 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?

Three sentences, each contributing distinct information: scope, content coverage, and usage instruction. It is front-loaded with the purpose and avoids filler, though the middle sentence is dense with category lists that could be lightly restructured for scannability without losing value.

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 output schema, the description covers the main needs: what the tool returns (dataset code, contents, window parameters), how to filter (search keyword), and when to use it (before query_dataset). It does not detail the exact output format, but that is not essential for this simple listing 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?

The schema description covers 100% of the single parameter, already explaining the case-insensitive keyword matching against code and title with examples. The description's phrase 'Search by keyword' adds no new semantic meaning beyond what the schema provides, so the 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 tool as a directory ('Directory of all 84 Elexon BMRS Insights datasets'), specifies the resource (datasets) and its exact relationship to query_dataset, making it immediately distinct from sibling tools like query_dataset, elexon_system_prices, or generation_by_fuel. The verb and scope are specific and unambiguous.

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?

It explicitly states when to use the tool: 'Search by keyword to find the code for a subject before calling query_dataset.' This gives the agent a clear, actionable condition and links to the primary sibling, while also implying a discovery role. No other alternatives are mentioned, but the guidance is concrete and sufficient.

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