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

Annotations already cover the read-only/idempotent/non-destructive profile, so the description's added value is the period-window inclusivity rule, the series' own date format, and the fact that each series carries its base period and method. Those are genuine behavioral details beyond the annotations, though coverage scope (which years exist) is unstated.

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?

Purpose is front-loaded and the parameter notes are dense but each earns its place. The trailing fragments ('UK-wide; ... UK only. Free.') are slightly choppy but still informative rather than 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?

With an output schema present, return values needn't be detailed, and the description still mentions base period and method. Required parameter, date formats, frequency, and geographic limits are all covered; the only soft spot is the open-ended sector list.

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 0%, so the description must carry the load, and it does: it enumerates all four basis values matching the enum, gives sector examples, the freq options, and the exact period token formats (2014Q1, 2014M01, 2014) for from_period/to_period that the schema titles alone do not convey.

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 gives a specific resource (construction cost index series) and its domain role ('for a development appraisal's cost side'), and it indirectly distinguishes itself from site_appraisal by noting regional factors are handled there. It does not explicitly differentiate from the closest sibling, build_cost, so it falls short of a 5.

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?

Usage context is clear (cost side of a development appraisal) and constraints are stated: UK-wide, UK only, free. It routes regional work elsewhere ('regional factors come with the site appraisal'), but never states when to prefer build_cost or the other index series siblings.

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