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

With no annotations, the description carries the full behavioral disclosure burden. It adds meaningful caveats: the registry only checked the 'classical half' of each card, so it is 'never a trust oracle', and listings 'age out after 30 days'. This goes well beyond a simple listing description.

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 sentences with the core return shape and scope front-loaded. The trust caveat and age-out policy are compact and relevant. Every sentence earns its place with no filler.

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 zero-parameter read tool with no output schema, the description covers the return shape ({card, at}), public invariance, freshness (30 days), and the critical trust limitation with verification alternatives. Nothing essential is missing for an agent to call and interpret the tool correctly.

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 tool has zero parameters and schema coverage is 100%, so there are no parameter semantics to clarify. The baseline of 4 applies because no parameter documentation is needed and the description does not need to compensate for any schema gaps.

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 identifies the tool as a read-only view of current public market listings, stating 'Every current listing {card, at}' and 'the public listing set' in the title. It distinguishes itself from user-specific market operations by emphasizing that the data is 'identical for every reader', though it does not explicitly name a sibling tool it is not.

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: use this to see the public listing set, and it points to alternatives for verification (SDK credentialVerify or null_market_browse). However, it does not explicitly state when to prefer this tool over sibling market tools like null_market_list or null_market_delist.

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