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

Beyond the readOnly/idempotent annotations, it discloses the return shape ('several codes come back joined by newlines') and the auth posture ('no API key, no account, no sign up'), both of which the annotations do not convey. It does not say what happens when no code is found, which keeps it from a 5.

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 short sentences, front-loaded with the core action and formats, then return behavior, then auth reassurance. Nothing is redundant or buried.

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 simple two-parameter read tool with no output schema, the description covers formats, input choice, return encoding, and auth. Only the empty-result / error case is left unspecified, a minor gap given the tool's simplicity.

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% and both parameters are already well documented, including the 24-hour expiry and the size limit. The description's 'Give image_base64 or storage_id' only restates the either/or choice already implied by the schema, adding no size, format, or expiry detail.

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 ('read') and resource ('QR codes') plus the exact accepted image formats (PNG, JPEG, GIF, WebP), which cleanly separates it from the sibling create_qr_code. An agent can pick it without opening the schema.

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 tells the caller to 'Give image_base64 or storage_id', which is input guidance rather than when-to-use guidance. There is no explicit statement of when to prefer storage_id over base64 (that lives only in the schema) and no when-not or alternative-tool routing, so usage is only implied.

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