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

Beyond the annotations, the description discloses important behavior: it replaces any existing QR on the card, refuses USPS clear-zone positions, falls back to bottom-right when no QR slot exists, and shows a preview. These details materially help an agent predict the tool's side effects and recovery path.

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 front-loaded with the core action and remains organized around placement, replacement, and prerequisites. It is slightly dense and long for a tool definition, but nearly every sentence carries useful operational detail for a complex placement operation.

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?

Given six parameters, no output schema, and placement-sensitive behavior, the description covers the key invocation details: prerequisites, fallback placement, rejected zones, replacement behavior, and preview. An agent has enough information to call it correctly without needing further clarification.

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 already 100%, but the description adds real meaning beyond the schema: it explains what `position="auto"` actually targets, how corners and `x_inches`/`y_inches` are interpreted, and why `size_inches` matters for scan reliability. This is substantive parameter guidance, not repetition.

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 states a specific verb and resource: put a tracked QR code on the back of the user's postcard template and show the preview. It clearly separates this from QR creation (`spur_create_qr_code`), QR listing, and tracking activity (`spur_get_qr_code_activity`).

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?

It gives an explicit prerequisite: create a QR code first with `spur_create_qr_code` if `spur_list_qr_codes` has none that fits. It also gives corrective guidance if placement overlaps message text and explains the automatic fallback when no QR slot exists.

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