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

Annotations already declare readOnly, idempotent, non-destructive, so safety is covered. The description adds non-obvious domain behavior beyond that: which fields are absent and where they live, and the currency-denormalization caveat that would otherwise cause a wrong answer. It doesn't discuss pagination/error behavior, but for a single-record read that is minor.

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 sentences, all front-loaded with the core definition first and the caveats after. Every sentence carries distinct information (identification, field boundaries, currency), though the parenthetical UI path is slightly extraneous.

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 compensates by enumerating returned fields (amount, date, receipt, linked project or work order) and the fields it omits plus where they live. Combined with the currency caveat, an agent has everything needed to call and interpret the result.

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 there is a single UUID-typed id, fully documented in the schema. The description only restates 'by ID' and adds no format, scoping, or lookup semantics beyond what the schema provides, so baseline 3 applies.

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+resource (get a project-scoped expense by ID) and even locates it in the UI (Project → Costs → Expenses tab). It explicitly names the sibling it is not (get_asset_cost) and the record type it excludes, so an agent can distinguish it from the other cost/expense getters without opening 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?

Explicitly routes the agent: use get_asset_cost for records carrying invoice_number/po_number, and call get_organization_settings for currency_code before stating an amount. Both the alternative and a prerequisite are named with their triggering conditions.

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