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

Annotations already mark the tool as read-only and non-destructive. The description adds meaningful behavioral context: results are newest-first and 'joined to the live listings,' implying current listing state is reflected rather than a stored snapshot. It also discloses the auth requirement.

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?

A single, front-loaded sentence conveys the resource, ordering, join behavior, and auth requirement with no filler. Every word adds information.

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-only list tool with safety annotations, the description covers everything needed to invoke it correctly: scope, ordering, live-join behavior, and auth. The lack of an output schema is a minor gap for a simple favorites-list tool.

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 input schema has zero parameters, so this dimension sits at the baseline of 4. There is no parameter detail for the description to add or clarify.

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 resource ('favorited registry listings') and the operation (listing them), adding valuable specifics like newest-first ordering and live join semantics. This differentiates it from action-oriented siblings like registry_favorite and search-oriented registry_search.

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 context is clear: this is for the authenticated user's saved favorites, and the description explicitly states the required Authorization header. It does not explicitly name alternatives or state when not to use it, so it stops short of a 5.

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