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

Annotations already declare destructiveHint=true, idempotentHint=true and openWorldHint=false, so the description's safety lines largely restate them, though it does add real nuance: previous values are not preserved or restored, and scope is limited to the authenticated account and accessible trips. The critical gap is that it never says whether 'data' is a partial merge (unmentioned fields untouched) or a replacement (unmentioned fields cleared), which matters most for a destructive update.

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 sentences, verb and target front-loaded, with the safety caveats compactly labeled. Slight redundancy with the annotation block keeps it from being maximally efficient, but nothing is padded.

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?

An output schema exists, so return values need not be explained. However, for a destructive update over a free-form 'data' object, the description should clarify partial-vs-full replacement and error behavior on an invalid id; those omissions leave a meaningful hole for an agent deciding how to call it.

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 id and trip_id are already documented, giving a baseline of 3. The description adds nothing about the 'data' payload — it does not list which expense fields are updatable or how they are encoded, even though 'data' is an open-ended object with additionalProperties=true where the schema is least helpful.

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 ("Update a Tripsy expense") plus the lookup key ("by id"), so it is distinguishable from tripsy_expenses_create/delete/list/show. It stops short of explicitly contrasting itself with siblings such as show or delete, but the operation is unambiguous.

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?

Usage is only implied: an agent can infer it should be used when modifying an existing expense that already has an id. There is no guidance on prerequisites (e.g., calling tripsy_expenses_show first to obtain current values), no statement about when to prefer delete+create, and no exclusions.

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