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

Annotations already declare readOnly/idempotent/non-destructive and open-world, so the safety profile is covered. The description adds genuinely non-structured context: 'Quota-charged; cached results are free' and the GB-only, digitally-filed precondition. It stops short of describing failure behavior when accounts aren't digital or available.

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 dense sentences, front-loaded with purpose, followed by destination and constraints. 'Saves typing seven numbers from a PDF' is a value proposition rather than filler, and no sentence is redundant.

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 still conveys the shape of the return ('seven numbers', 'comparatives exactly as filed') and where they land, plus quota/caching and jurisdiction limits. Minor gap: it doesn't say what happens on quota exhaustion or non-digital filings.

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?

Only one parameter exists and schema coverage is 100%, so the schema fully documents companyNumber (though it doesn't explain the GB number format). The description says nothing about the parameter itself; baseline 3 applies when the schema carries the load.

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 and resource ('Read last year's figures out of the company's last filed accounts at Companies House') and ties the output to concrete downstream consumers (check_accounts, save_filing *Prior fields). An agent can distinguish it from siblings like lookup_company or dormant_figures without opening any schema.

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?

Explicitly scopes use ('GB only, and only when the last accounts were filed digitally') and names exactly where the result should be dropped. Both the when and the when-not conditions are given, leaving nothing to inference.

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