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

Annotations already declare readOnlyHint=false, destructiveHint=true, idempotentHint=true, and openWorldHint=false, so the safety profile is covered. The description usefully adds the required scope (expenses:write), which annotations cannot express, but it omits the critical partial-vs-full update semantics (are omitted fields cleared or preserved?) for a tool flagged destructive.

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?

Two short sentences, both front-loaded and informative: the operation and target come first, the authorization requirement second. There is no filler, hedging, or repetition of the schema.

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 a fully documented schema and annotations carrying the destructive/idempotent profile, the definition is minimally complete, and no output schema means return values need not be described. The missing piece is update semantics for optional fields, which matters given destructiveHint=true.

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 100% across all nine parameters, so the schema documents each field adequately and the baseline is 3. The description adds nothing about parameter behavior, such as whether the nine optional fields are partial-patch or full-replace, which is the one gap the schema leaves open.

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 ('Update an existing expense by ID'), so an agent can distinguish it from create_expense, get_expense, and delete_expense without opening the schema. However, it does not name or differentiate itself from the closely related bulk_update sibling, which is the main ambiguity risk.

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 description gives a precondition ('Requires expenses:write scope') and the 'existing...by ID' phrasing implies this is for modifying already-created records, but there is no explicit when-to-use vs. bulk_update/update_project_time_entry style guidance and no when-not-to-use exclusions.

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