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

Annotations already establish read-only, idempotent, open-world behavior, but the description adds genuinely new operational facts: private/local addresses are refused (SSRF guard) and the decoded payload is capped at 10 MB. It also discloses the no-code edge case, which no structured field covers.

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?

Four short sentences, zero padding, with the core action front-loaded and the constraints and return shape following in priority order. Every sentence carries information an agent needs.

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?

Input modes, security restriction, size limit, return shape, and the empty-result edge case are all covered, and an output schema exists so detailed return formatting need not be repeated. Nothing material is missing for correct invocation.

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%, so baseline is 3. The description goes slightly beyond by clarifying that either base64 data or a public URL satisfies the single required 'file' object, and it restates the url-side private-address restriction and the data-side 10 MB cap in the context of the call.

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: 'Read QR codes and barcodes from an image.' That clearly separates it from write-side siblings like generate_qr_code. It stops short of naming the nearest ambiguous sibling (read_image_text, which does OCR rather than code decoding), so an agent must infer the boundary.

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?

'Send base64 or a public URL' tells the agent how to supply input, and the private-address refusal plus 10 MB cap narrow the usable cases. However, it never states when to pick this over read_image_text or other image tools, so the usage guidance is implied rather than explicit.

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