validate_upi_vpa

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

Annotations already indicate the tool is read-only and idempotent (readOnlyHint=true, idempotentHint=true). The description adds valuable context: it 'decodes known provider handles,' which implies the tool provides additional information beyond a simple pass/fail. There is no contradiction with annotations, and the description enhances understanding of the tool's output.

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 extremely concise with two sentences. The first sentence states the core function, and the second explains when to use it. Every word is meaningful, and the information is front-loaded. No unnecessary text.

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?

Given the simple input schema (one parameter), clear annotations, and the presence of an output schema (as indicated by context signals), the description provides the necessary context for an agent to decide when to call the tool. It could briefly mention that it does not validate against live systems, but the current description is largely adequate.

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 100% (the 'vpa' parameter already includes a description and example). The tool description does not add new semantic information about the parameter beyond what the schema provides. Baseline is 3, and no extra value is added.

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's function: 'Validate UPI VPA structure and decode known provider handles.' It uses a specific verb ('validate') and resource ('UPI VPA'), and distinguishes itself from sibling tools (e.g., validate_pan, validate_gstin) by focusing on UPI addresses. The additional context about 'before payment routing' reinforces the specific use case.

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 provides explicit guidance: 'Use when checking whether a UPI address is structurally valid before payment routing.' This tells the agent when to use the tool. While it does not explicitly state when not to use or mention alternatives, the sibling list makes it clear that this is the only tool for UPI VPA validation, so the guidance is sufficient.

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