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

Beyond the readOnlyHint annotation, the description reveals important behavioral context: the returned image content block is the display itself, the client renders it directly, and sandboxed widget environments block external hosts. This explains why custom HTML should be avoided and adds value beyond the safety hint. It also discloses supported sizes/formats, which is useful for caller expectations.

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 two sentences and front-loaded with the core purpose. The second sentence is long but packs critical rendering guidance and optional parameter details without redundancy. Every phrase earns its place, though the size list is somewhat lengthy and could be trimmed or rephrased for clarity.

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?

The description covers the main behavior, display instructions, and optional parameters, and an output schema exists so return format need not be explained. However, it does not clarify how a caller specifies which card (e.g., id vs. name) when both are optional, nor does it describe default behavior when no setCode/version is provided. This is a notable gap for a tool with four optional parameters.

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?

With schema description coverage at 0%, the description carries the burden. It explicitly explains setCode (specific printing) and lists size/version options (small, normal, large, png, art_crop, border_crop, etc.), which appear to map to the 'version' parameter. However, it does not explain 'id' or 'name' parameters, nor does it clearly connect the 'size' list to the schema's 'version' field, leaving some ambiguity about which parameter controls which aspect.

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 opens with 'Fetch a card's image,' a specific verb+resource pair that clearly states the primary action. It distinguishes itself from siblings like get_card (card data) and get_card_printings (printing list) by focusing on the image retrieval and display. The optional setCode and size details reinforce the scope.

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 ('Fetch a card's image') but does not explicitly contrast with alternatives or state when not to use it. It provides guidance on how to display the result (as a content block) and warns against custom HTML, but these are post-fetch behaviors rather than tool-selection criteria. No direct comparison to sibling tools is offered.

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