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

Annotations only say destructive=true and idempotent=true; the description goes well beyond that by disclosing concrete side effects: changing the address clears the test, the new address becomes what supporters are quoted and what past supports display, and disabling the default shifts quoting to the lowest active ID. The minimum-one-active invariant is also a real constraint an agent must respect.

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, front-loaded with the operations list followed by consequences. No filler and every clause carries either a capability or a side effect.

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 annotations covering safety and an output schema covering returns, the description supplies the missing behavioral layer. It could still say that updates are partial (only id required, other fields optional) to clarify how multi-field edits compose, but nothing critical is absent.

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 only 20% (testDone alone), so the description has to carry the load: it maps address->vpa, label, on/off->active, and the one-rupee test->testDone, and adds downstream meaning for vpa that the schema lacks. It still omits the expected VPA format and label constraints, so not a full 5.

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 (change) and resource (UPI ID) and enumerates the exact mutation surface: address, label, on/off state, and test-done flag. That scope cleanly separates it from add_upi_id, remove_upi_id, set_default_upi_id, and set_upi_rotation without needing to name them.

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?

It gives clear operating context and constraints (at least one ID must stay active, switching off the default promotes the lowest active ID), which tells the agent when a call is legal. It does not, however, explicitly route the agent away from siblings like set_default_upi_id or remove_upi_id for those specific operations.

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