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

Annotations cover the safety profile (readOnlyHint, openWorldHint, idempotentHint=false), and the description adds genuinely useful non-annotation context: the return format (SVG plus data: URL), the 2,000-character ceiling, and the cost model ($0.001 USDC via x402 or prepaid credits, free trial). Pricing and invocation-cost disclosure is exactly the kind of behavior an agent needs before calling a paid tool.

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 front-loaded sentences: what it does, what it returns, then options/limits/price. Every clause carries information an agent needs and there is 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?

With a full input schema and an existing output schema, the definition need not explain return values, yet it usefully names the return types and the payment path. Complete enough for a 6-parameter, 1-required tool; only the absence of any failure-mode note (e.g. invalid hex or over-length input) keeps it off a 5.

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 the schema already documents ecc, size, margin, dark/light, and the 2000-char limit. The description's option list (ecc, size, margin, dark/light, 2000 chars) largely restates the schema without adding format, default, or interaction detail, so 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 ('Turn text or a link into a QR code') and is instantly distinguishable from every sibling in the list, none of which generate QR codes. The follow-up sentence about the SVG and data: URL output confirms the deliverable concretely.

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 clear usage context — encode text/URLs and drop the result into HTML or Markdown — but offers no explicit when-not or alternative routing. Because no sibling overlaps this function, the lack of an exclusion clause is a minor gap rather than a real ambiguity.

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