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

Annotations already declare readOnlyHint=true, openWorldHint=true, idempotentHint=true, and destructiveHint=false, so the safety profile is fully covered. The description adds value beyond annotations by disclosing the API version (beta CMD API), the data source, the licensing (Open Government Licence v3.0), and the exact fields returned. It doesn't mention pagination behavior beyond the offset parameter, but the schema already documents that. A 4 is appropriate because the description enriches the behavioral context without contradicting 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 three sentences, each earning its place: the first states the core function and return fields, the second gives keyword usage examples, and the third routes to related tools and cites the source/license. It is front-loaded with the most important information and contains no filler.

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 list/search tool with a full output schema, complete parameter documentation, and comprehensive annotations, the description covers everything an agent needs: what it returns, how to filter, how to use the results with other tools, and the data source. The output schema handles return-value details, so the description need not repeat them.

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 fully documents all three parameters (limit, offset, keyword) with types, ranges, defaults, and examples. The description adds the keyword usage guidance with topic examples, which is helpful but not essential. Baseline 3 is correct because the schema does the heavy lifting and the description provides marginal additional value.

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 ('List and search'), a precise resource ('all 337+ datasets published by the UK Office for National Statistics'), and the API source ('beta CMD API'). It also enumerates the returned fields (dataset IDs, titles, descriptions, timestamps, frequencies, national statistic flags), which clearly distinguishes it from sibling tools like ons.stats.gdp or ons.stats.cpih that fetch specific statistical series rather than the dataset catalog.

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 tells the agent when to use this tool: to list/search the ONS dataset catalog, and how to filter by topic using the keyword parameter with concrete examples. It also directs the agent to use dataset IDs with other ons.* tools or the ONS Cantabular API, providing clear routing guidance. This is more explicit than most sibling definitions.

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