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

Annotations already declare readOnlyHint, idempotentHint, and openWorldHint, so the safety profile is covered. The description usefully adds the shape of the response (regulatory status, business type, registered address), but says nothing about rate limits, auth behavior, or fallback when the FRN is unknown.

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 tight sentences: the purpose and return fields are front-loaded, followed by a concrete invocation example. No filler.

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 lookup with full schema coverage and no output schema, the description supplies what the schema cannot: the list of returned attributes. Nothing essential is missing, though noting sibling alternatives or miss behavior would complete 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 description coverage is 100% and the frn parameter already carries an example plus an _apiKey explanation, so the schema does the heavy lifting. The description's inline example call adds minor reinforcement but no new semantics.

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 (look up) and resource (FCA-regulated firm) with the exact lookup key (FRN) and enumerates the returned fields. The FRN keying implicitly separates it from the sibling fca_firm_search, though no sibling is named explicitly.

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?

Usage is implied by the required FRN key, but there is no explicit when-to-use or when-not-to-use guidance and no mention of the name-based alternative fca_firm_search for agents who lack an FRN.

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