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

With annotations already declaring readOnlyHint=false and destructiveHint=true, the description adds real context beyond them: permission requirements, the owner-only markup restriction, and the clarification that nothing is paid. It does not, however, explain the somewhat surprising destructiveHint=true for a create operation or any side effects on billing aggregation.

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 front-loaded sentences: purpose first, then the cost-vs-payment scope clarification, then permission constraints. It is efficient, though the field enumeration in sentence one partly duplicates what the schema exposes.

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 9-parameter mutation tool with no output schema, the description covers purpose, field meaning, defaults implied by schema, and role requirements adequately. A brief note on the returned identifier or validation behavior would be the only meaningful addition.

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 78%, so most parameters (day, amount, cardId, billable, markupPercent, database description) are already documented in the schema. The description largely re-lists the same fields and repeats the enum values already present in the schema, adding only marginal narrowing value.

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 names a specific verb and resource ('Logs an expense on a project') and enumerates exactly what the expense captures, so an agent can distinguish it from siblings like create_invoice, log_time, or create_task without opening schemas. The scope note 'It records a cost; nothing is paid' further sharpens the intent.

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 states concrete prerequisites and constraints — 'Needs the editor role on the project' and 'Only the project owner can set a markup' — which tell the agent when it can and cannot use the tool. It does not name sibling alternatives (e.g. delete_expense, update_expense, create_invoice), so it stops short of explicit alternatives.

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