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

Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=true, so safety is covered. The description adds genuinely new behavioral context beyond the annotations: a 10 MB upload ceiling, supported formats, the paid-plan corner-coordinate feature, and an explicit 10-credit cost. That cost and size disclosure is exactly the kind of context annotations can't express.

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?

A single dense sentence that front-loads the core action and appends constraints and cost in parentheticals. Slight redundancy from restating the tool name twice at the start, but no wasted content overall.

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 decoding tool with an output schema that already defines return values, the description covers action, input constraints, cost, and the premium output field. Nothing essential to correct invocation is missing, though the lack of sibling routing guidance is a minor residual gap.

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% and the formats are already documented in the schema, so the baseline is 3. The description earns one more point by adding the 10 MB size limit, which is not present in the schema and is a real constraint the agent must respect when supplying an image.

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 (decodes) and resource (QR code images), and specifies what is extracted (text, web links, raw payload). It doesn't name the obvious sibling BarcodeReader, so an agent must infer the QR-vs-barcode distinction from the tool name alone, but the purpose itself is unambiguous.

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?

Usage is implied through the input requirements (send a JPG/PNG/GIF QR image), but there is no explicit statement of when to prefer this over BarcodeReader or when to use QRCodeGenerator instead. The agent gets enough to act, but nothing that routes it among similar siblings.

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