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

Beyond the annotations (readOnlyHint=false, idempotentHint=true, destructiveHint=false), the description discloses a real side effect: changing the address clears the one-rupee verification because it proved the old address. It also states the active-count invariant. It adds genuine behavioral context, though it says nothing about auth or failure modes.

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 tight sentences: purpose first, then two behavior/constraint notes. Every sentence carries information and nothing is redundant or buried.

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 and safety annotations exist, so return values and the read/write profile are already covered. The description supplies the mutation side effect and invariant an agent needs; only auth/permission requirements are unaddressed, a minor gap for this tool.

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?

With only 20% schema coverage, the description compensates by mapping 'address' to the vpa parameter, 'label' to label, and 'switch on or off' to active, and it ties the one-rupee check (testDone's concern) to address changes. Four of five parameters gain meaning not present in the schema, though the id parameter is left implicit.

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 states specific verbs and resource: changing the address or label of a UPI ID, or toggling it on/off. It clearly maps to the update operation, distinguishing it from add_upi_id and remove_upi_id by the word 'Change'. It stops short of naming siblings explicitly, but the purpose 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?

The description gives an invariant ('At least one ID has to stay active') that constrains when a toggle-off is valid, but it never names alternatives such as add_upi_id/remove_upi_id/set_default_upi_id or states when to prefer this over them. Usage is implied rather than explicit.

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