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

The annotations already signal a write operation (readOnlyHint=false) and the description is consistent with that by saying 'Add'. It adds a small amount of behavioral context—the expense is scoped to the signed-in user and may be attached to a project—but it does not disclose side effects like approval workflows or record creation details.

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 sentence that leads with the action and resource, then adds ownership scope and the optional project detail. There is no filler or redundancy.

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 six parameters, no output schema, and minimal parameter coverage, a one-sentence description leaves important context missing, such as valid project sources, activity type semantics, and any post-create flow. The agent is not fully equipped to invoke this tool correctly beyond the literal schema.

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?

Only 17% of the schema properties have descriptions, so the description must compensate, but it only clarifies that project_id is optional. The meaning of activity_type_id, is_billable, and the description field is left undocumented, and amount's semantics are not enriched beyond the schema constraint.

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 uses the specific verb 'Add' with the resource 'expense', identifies the owner scope as the signed-in user, and notes the optional project attachment. This clearly distinguishes it from siblings like timelog_update_expense and timelog_delete_expense based on action alone.

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 usage is implied: an agent can infer this tool is for creating expenses because it says 'Add an expense.' However, it does not explicitly route away from alternatives such as timelog_update_expense or timelog_approve_expense, nor does it state when not to use it.

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