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

Annotations already mark this as read-only and idempotent; the description adds meaningful behavioral context: no auth required, data source, licence, monthly frequency, and seasonal adjustment. It also clarifies the return window behavior ('most recent N months') without contradicting the 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 with no filler: definition, return behavior, and provenance/licensing. The most important identification details are front-loaded, and every sentence earns its place.

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 single-optional-parameter read-only tool with output schema and rich annotations, the description covers what the data is, how many points are returned, the source, licensing, and auth requirements. There are no material gaps an agent would need to resolve before calling it.

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 coverage is 100%, and the schema fully documents last_n (min, max, default, monthly cadence). The description's 'default 24, max 120' repeats schema information rather than adding meaning, so the baseline of 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 names a specific, measurable resource ('Monthly 12-month growth rate of UK M4 money supply') and pins it down with series ID, seasonal adjustment, and source. This clearly distinguishes it from rate-focused siblings like bank-of-england.rates.bank_rate and from non-UK money supply tools.

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 provides clear context for when to use the tool (any request for UK M4 money supply growth), including frequency and adjustment details. It doesn't explicitly name alternatives or exclusion conditions, but the resource definition is specific enough that an agent won't confuse it with other tools.

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