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

With no annotations, the description carries the burden. It discloses quota charges ('Quota-charged; cached results are free') and accuracy ('gets the comparatives exactly as filed'), which are valuable beyond the obvious read behavior. It doesn't cover error handling or edge cases, but the cost and accuracy notes add real context.

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?

The description is a compact paragraph that front-loads the primary purpose, then layers usage context, conditions, and cost in a logical order. Every sentence earns its place with no redundancy.

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 simple read tool with one parameter and no output schema, the description explains the output's purpose (drop into *Prior fields), the conditions (GB, digital filing), and cost. It could mention what happens if accounts aren't available, but overall it's complete enough for an agent to call it correctly.

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% with a single parameter described as 'The GB company number.' The description reinforces the GB scope, but adds no new semantic detail beyond what the schema already provides. Baseline 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 ('Read') and resource ('last year's figures out of the company's last filed accounts at Companies House'), and clarifies its role as a helper for check_accounts and save_filing. It clearly differentiates from siblings by specifying it populates *Prior fields and is GB-only.

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?

It provides explicit usage conditions: GB only, last accounts filed digitally, and positions it as a time-saver over manual PDF entry. It doesn't name alternative tools or state when not to use it, but the context is clear and actionable.

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