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

Annotations declare readOnlyHint=false and destructiveHint=false, indicating a non-destructive mutation. The description goes beyond that by explaining that a favorite is a POINTER and that running/scheduling adopts a runner-owned copy on demand—key behavior that affects how the agent should reason about the tool's side effects. It also discloses the Auth requirement. No contradiction with annotations.

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 three sentences long, front-loaded with the core purpose, then the pointer nuance, then the unsave flag and auth requirement. There is zero fluff or redundancy—every sentence earns its place.

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 tool with only 3 parameters, no output schema, and annotations covering the mutation safety profile, the description is highly complete. It covers purpose, when to use, pointer semantics, unsave behavior, and auth. It doesn't mention potential error cases or idempotency, but these are minor gaps 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?

The schema already documents all three parameters with 100% coverage, so the baseline is 3. The description adds value by telling the agent to find provider_id and external_id via registry_search, and by explaining the remove:true flag (though that's also in schema). This goes slightly beyond a simple repetition of the schema, earning a 4.

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 uses a specific verb and resource: 'Save any registry listing ... to your Favorites' and explicitly includes the unsave case via remove:true. It distinguishes from siblings by stating it applies only to listings you didn't author, and references registry_search and the pointer/adopt behavior, making it clear it's a bookmarking tool rather than a search or adoption tool.

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 agent when to use this tool (to save or unsave a listing you didn't author) and how to locate the required IDs via registry_search. It doesn't explicitly state when *not* to use it (e.g., for your own listings) or compare it directly to registry_adopt, but the pointer explanation implies the difference. Overall, it provides adequate context for selection.

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