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

Annotations cover the safety profile (idempotent, non-destructive, closed-world), and the description adds real behavioral context beyond them: other IDs stay on the account, and a default set on an inactive ID is never actually quoted. This edge-case disclosure is exactly the kind of value the description should add.

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 short sentences, front-loaded with the primary effect and followed by the caveat. The 'does not switch an ID on' clause and the 'inactive ID ... never quoted' clause partly restate the same point, a small 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?

For a one-parameter mutation with annotations and an output schema, the description covers the essential gotcha (inactive IDs are not activated by being made default). It omits error/permission behavior and how to discover the ID, but nothing critical to correct invocation is missing.

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 0% and the single 'id' parameter is undocumented, but the description's 'one active UPI ID' framing lets an agent infer the parameter is a UPI ID. It still does not say where to obtain the ID (list_upi_ids) or that the target must be active, so it only partially compensates for the coverage gap.

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 effect ('Make one active UPI ID the one supporters are shown first'), which is clear enough to distinguish from update_upi_id, add_upi_id and set_upi_rotation. It does not name any sibling explicitly, so it stops short of the 5-level differentiation.

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?

No when-to-use or when-not-to guidance is given, and no alternative is named (set_upi_rotation governs ordering among IDs and is the closest sibling). The only guidance is an implicit constraint that this reorders rather than adds or removes IDs.

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