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

Beyond the readOnly/idempotent annotations, it discloses the crucial limitation that it cannot check that the sheet balances (retained earnings is the balancing figure), the cross-column reserves comparison warning and its likely meaning, free/instant cost, and major-units convention. This is rich behavioral context the annotations cannot convey.

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?

Dense but front-loaded: purpose, then return values, then the two limitation/comparison caveats, then cost and currency. The 'Do not tell anybody their sheet was checked...' sentence is slightly discursive but carries an important framing constraint; overall tight for the amount of critical guidance.

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?

No output schema, yet the description fully describes the return (derived current/prior-year sheet, rejected figures, completeness flag) and the warnings from lastFiledAs. An agent has everything needed to call and interpret 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 coverage is 100%, so baseline is 3, but the description adds meaning to lastFiledAs (source is lookup_company's company.lastAccountsType, and what it triggers: a dormant-filing warning) and clarifies major-unit currency. That is genuine value beyond the schema.

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: 'derive a small-company balance sheet... from raw figures and validate it', with the exact return contents enumerated. This clearly distinguishes it from siblings like explain_accounts or totals_to_figures.

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?

Explicit 'call it after every change to the figures', plus instructions to pass lastFiledAs from lookup_company rather than guessing. It also carves out what it does not do, preventing misuse.

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