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

With no annotations provided, the description carries the full behavioral burden. It discloses the input format (PNG base64), the operation (decoding), and the output (raw payload and content type). This goes beyond the tool name, though it omits potential error cases or side-effect statements, which are less critical for a simple decode operation.

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 a single, information-dense sentence that starts with the primary action and includes essential output details. Every word contributes, with no fluff or repetition.

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 tool with one parameter and no output schema, the description covers both input and output, including a list of expected content types. It is self-contained and sufficient for an agent to understand the tool's behavior and expected results.

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?

The schema already provides 100% coverage with a detailed description of image_base64. The description adds a brief mention that the input is a PNG image in base64, but this largely repeats what the schema states. Since schema coverage is high, a baseline of 3 is appropriate, and the description adds marginal extra meaning.

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 with a specific verb and resource: 'Decode a QR code from a PNG image'. It also mentions the return value (raw payload and content type), and the sibling tools (e.g., generate_qr) confirm the distinct purpose of decoding vs generation.

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 implies usage by its contrast with sibling tools like generate_qr, but it does not explicitly state when to use this tool over alternatives or any exclusions. There is no mention of prerequisites or when not to use it, so guidance is merely implied.

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