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

Annotations already declare readOnly/idempotent/non-destructive, and the description adds genuinely new behavioral facts: nothing is persisted, no money moves, and the payer approves in their own app. It also discloses the full set of return artifacts (PNG, upi:// link, printable poster page) that the agent would otherwise not know about, since there is no output schema.

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 sentences, front-loaded with the core output and use case, then the side artifacts, then the safety boundary. Minor redundancy in "PhonePe, Google Pay, Paytm, BHIM and every UPI app can scan," where the enumeration largely restates "every UPI app."

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 no output schema, the description carries the burden of describing returns and does so explicitly (PNG image, upi:// link, download page). Combined with the no-storage/no-money-movement disclosure for a read-only tool, an agent has everything needed to call it and set payer expectations.

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%, so all five parameters including the amount/note optionality and size default are already documented in the schema. The description only restates that amount and note are optional, adding no format or constraint detail beyond the structured fields — the baseline 3 applies.

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?

States a specific verb and resource ("Generate a UPI payment QR code (PNG image)") plus the scope: an Indian UPI VPA, optional fixed amount and note. It is clearly separable from siblings like create_upi_payment_link and read_upi_link, since the output is a scannable image artifact rather than a link record.

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?

"Optionally with a fixed amount and note... Leave it out and the payer types the amount" gives clear context for the two modes of use, and "Nothing is stored. It never moves money" rules out the collection/settlement use case. It never explicitly names an alternative sibling or says when to prefer create_upi_payment_link instead, so it stops short of full routing guidance.

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