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

Annotations already declare readOnly, idempotent, non-destructive, non-open-world, so the safety profile is covered. The description adds genuine behavioral value by enumerating what the record contains (amount in NZD, liability people, reconciliation status), which matters because there is no output schema. It does not mention error behavior for a missing id, keeping it from a 5.

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?

A single front-loaded sentence that leads with the core purpose before the field enumeration. The long list of fields is slightly listy but earns its place since no output schema exists to convey the return shape.

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 read-only single-record fetch with no output schema, the description adequately covers both the input source (id from list_expenses) and the expected return contents. Only the failure mode for an unknown id is absent, which is a minor gap.

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 both parameters are already documented in the schema, including the conditional organisation_id rule. The description reinforces that the id comes from list_expenses but adds no syntax or format detail beyond the schema, so the baseline 3 is correct.

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 ('Get'), resource ('expense record'), and scope ('in full, by its id'), and distinguishes itself from the sibling 'list_expenses' by naming it as the source of the id. An agent can tell this single-record fetch apart from the list tool without opening either schema.

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 phrase 'by its id from list_expenses' establishes the workflow context for when to call this tool (after listing expenses) and where the required id comes from. It stops short of an explicit exclusion such as 'use list_expenses when you do not already have an id', so it is clear context without full when/when-not guidance.

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