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

Annotations already declare readOnly/idempotent/non-destructive/closed-world, so the safety profile is covered. The description adds real context beyond that: the NHS figure is a DHSC day-to-day proxy and the values are 'illustrative averages, not live spending rates' – a caveat that materially affects how an agent should present results.

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, front-loaded with the core action, and the two caveats that follow are non-redundant since one explains a proxy choice and the other guards against misinterpretation as live data. Slightly more prose than strictly needed but nothing wasted.

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 no output schema, the description compensates by naming the return shape (share, duration, comparisons against other budgets) and warning that values are illustrative averages. For a 2-param read-only calculator this is close to sufficient, though it doesn't state the output units or timeframe of the 'duration' figure.

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 both parameters (amount in GBP, budget enum with default 'nhs') are fully documented by the schema. The description adds only that the response 'also includes other budgets', which is output behavior rather than parameter meaning. Baseline 3 applies.

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 ('Express a GBP amount') and resource ('2025-26 public budget') plus the output form ('share and duration'). The 'comparisons against other budgets' clause distinguishes it from adjust_for_inflation and calculate_take_home, which do different arithmetic on amounts.

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 makes the use case inferable (converting a GBP figure into budget-relative terms) but never states when to pick this over adjust_for_inflation or calculate_take_home, nor any prerequisite. Usage is implied rather than guided.

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