validate_upi_vpa

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

The annotations declare openWorldHint=false, implying a closed, deterministic world context. However, the description states that NPCI handle lists evolve over time and that unknown handles are not auto-invalidated, which suggests the tool's recognition behavior depends on changing external state. This directly contradicts the openWorldHint annotation, so the behavioral transparency score must be minimal.

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?

The description is well-structured with clear Args, Returns, and Notes sections, and every sentence serves a purpose. It is compact and front-loaded with the core purpose before diving into details.

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 single-parameter tool with an output schema, the description covers the use case, argument format, return envelope fields, and a critical behavioral caveat about unknown handles. The only completeness issue is the contradiction with openWorldHint, which prevents the overall definition from being fully reliable.

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?

The schema already documents the VPA parameter with an example, but the description adds meaningful semantic guidance by specifying the exact username@handle format. The Returns note about a normalized VPA and known_provider flag also clarifies how the input parameter is used, exceeding what the schema alone provides.

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 clearly states the tool validates UPI VPA structure and decodes known provider handles. This is specific and effectively differentiates it from the sibling validation tools, which target different entities such as PAN, GSTIN, or Aadhaar.

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 explicitly says to use this tool when checking whether a UPI address is structurally valid before payment routing, which is a clear context. It does not explicitly rule out other tools or name alternatives, but the target domain is already distinctive enough among siblings.

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