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

Annotations already declare readOnly/idempotent/non-destructive, so the safety profile is covered; the description adds real value beyond that by stating the inspection output (payee, amount, note, merchant fields) and that it emits warnings for risky patterns like an AutoPay mandate posing as a payment. It doesn't say how warnings are surfaced (severity levels, pass/fail verdict), which keeps it below a 5.

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?

Two sentences: the first front-loads what is read and what is returned, the second gives usage. Every clause carries information (payee, amount, note, merchant fields, risk warnings, AutoPay caveat) with no filler.

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, read-only, no-output-schema tool, the description covers purpose, output content, risk warnings and usage triggers. The only gap is how the check result is shaped (verdict vs. list of warnings), which matters since no output schema exists to describe it.

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 100% for the single `link` parameter, and the schema description already says it is the upi://pay?… text decoded from a QR. The description only restates the format and adds the example context, so it neither compensates for a gap nor adds much beyond structured data — baseline 3.

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?

Specific verb + resource ('Read a UPI payment link… and check it') plus an enumeration of exactly what is extracted (payee, amount, note, merchant fields) and flagged (malformed/risky data, AutoPay mandate disguised as a payment). This clearly separates it from create_upi_payment_link and generate_upi_qr_code, which produce links/QRs rather than inspecting 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?

Gives two concrete trigger scenarios: 'before paying from a QR someone sent' and 'to find out why apps reject a QR'. It stops short of explicitly naming the alternative sibling (explain_upi_error) for the rejection-diagnosis case, so the routing between this tool and that one is left to inference.

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