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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, covering the safety profile. The description adds the constraint that 'now' refers to the latest stored observation, not a live price, and notes the coverage ranges for RPI and CPI, which is useful behavioral context. It doesn't mention rounding behavior explicitly (though the schema does), nor does it describe output format, but with annotations carrying the safety burden, this is adequate.

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?

Two sentences with no waste, front-loading the core purpose. The second sentence packs useful constraints about series and 'now'. Efficient and structured.

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 calculation tool with full schema coverage and annotations, the description is mostly complete. It covers series coverage and 'now' semantics, but doesn't mention output format (no output schema exists) or potential limitations like data availability beyond 2026. Adequate but could be more complete.

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 all parameters thoroughly. The description adds some meaning by explaining the 'now' value and series coverage, but largely repeats what the schema provides. Baseline 3 is appropriate when schema does the heavy lifting.

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?

States a specific verb (compare) and resource (GBP purchasing power between years). The title reinforces the verb+resource. It doesn't explicitly differentiate from siblings like calculate_take_home or compare_public_spending, but the purpose is clear enough.

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?

Provides important context about series coverage (RPI from 1948, CPI from 1988) and clarifies what 'now' means, which helps an agent choose the right series. However, it does not explicitly say when to use this tool versus the sibling tools, leaving some inference to the agent.

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