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

Annotations already declare readOnly, openWorld, idempotent, and not destructive. The description adds valuable context: no auth required, UK Open Government Licence, the series identifier, and the default/max range (90/1825 days). This goes beyond the structured annotations and clarifies usage constraints.

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 convey the purpose, series, parameter behavior, data source, licensing, and authentication. Every sentence earns its place; the most critical info (what it returns) is 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?

For a single-parameter read-only tool with an output schema, the description fully covers the series identity, data source, license, and parameter semantics. Nothing an agent needs to call it correctly is missing.

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?

The input schema already documents last_n with description including default (90), max (1825), and 'counting back from today'. The description repeats this info but adds nothing new. With 100% schema coverage, 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 states a specific verb ('Returns daily history'), a specific resource (SONIA), and identifies the exact series (IUDSOIA). This distinguishes it from sibling BoE tools like bank_rate and mortgage_2y_fixed without ambiguity.

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 implies usage for SONIA data but does not explicitly contrast with alternatives like bank_of_england.rates.bank_rate or other rate tools. There is no 'use this for X, use that for Y' guidance, so the agent must infer from the name and description.

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