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

The description adds a genuinely useful behavioral fact not present in annotations: a fixed price of $0.20 per call. Annotations already cover the side-effect profile (readOnlyHint=false, destructiveHint=false, openWorldHint=false), so the remaining gap is only the return shape, which the phrase 'list differences' loosely implies.

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 short fragments with the core action front-loaded and no filler. The final fragment is slightly elliptical (lacks an explicit subject) but still reads cleanly.

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 one-parameter comparison tool with no output schema and annotations that cover safety, the description covers action, inputs, cost and intent. The only omission is what the difference output looks like, which is minor given the tool's simplicity.

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% and the single parameter is documented as 'Two or more invoice texts.' The description's 'two or more invoices' corroborates but does not extend the schema — it doesn't clarify whether full raw text or extracted fields are expected, nor any length limits. Baseline 3 applies when the schema does the heavy lifting.

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 ('Compare two or more invoices and list differences') and scopes the comparison to amounts, tax and line items. Among the many fikra_compare_* siblings, the resource is unambiguous, so an agent can route to it without opening sibling schemas.

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 trailing phrase 'Spotting a changed amount, tax or line item across versions' implies the use case (version-to-version invoice diffing) but never states when to prefer this over fikra_compare_purchase_orders, fikra_reconcile_invoice_receipt, or fikra_extract_invoice_fields. Usage is inferable rather than explicit.

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