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

Annotations already declare readOnlyHint and openWorldHint, so safety is covered. The description adds genuinely useful behavioral context beyond annotations: pricing ($0.002 USDC per successful call), payment rails (x402 on Base/Solana/Arc), and the fact that failed calls are not charged. It omits rate limits or latency, which keeps it from a 5.

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 tight sentences: purpose/scope first, then a data-semantics disclaimer, then pricing. No wasted text; the most decision-relevant facts are front-loaded.

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?

Output schema exists, so return values need not be described, and the two-param read operation is fully covered by purpose, default series, and pricing disclosure. An agent could call it correctly from this alone; minor gaps are the lack of freshness/cadence notes for the daily series.

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%, with both params (days, series) fully documented including defaults in the schema itself. The description restates the default series and the N-day range but adds no syntax or format detail beyond what the schema already provides, so 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?

Clearly states the verb and resource: fetch Bank of England official daily statistics for a single IADB series over the last N days, sourced from the Bank's CSV download. Specifically names the default series (XUDLUSS) and disclaims interpretation, so an agent knows exactly what it returns. It does not explicitly contrast with the nearby central-bank siblings (norges_bank, bcb_brazil, world_bank), so sibling differentiation is only implicit via the name.

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?

'One series code over the last N days' implies the appropriate use case, and 'no interpretation of the series' hints at raw data retrieval. However, there is no explicit when-to-use/when-not guidance and no named alternative for other central-bank or macro data sources among the siblings.

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