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

Annotations already declare idempotentHint=true and destructiveHint=false, so the safety profile is covered. The description adds useful behavioral context: the favorite star is shared with the app and feeds list_viral_posts favorites_only, which is not obvious from annotations or schema.

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 a single, tightly written sentence that front-loads the action and resource. The parenthetical adds cross-tool context without wasting words.

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 two-parameter mutation with idempotent behavior already declared by annotations, the description is largely complete. It could add a bit more about response behavior, but the absence of an output schema and the simplicity of the operation keep the gap minor.

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 description coverage is 100%, with both post_ids and favorite clearly documented in the input schema. The description adds no additional parameter-level detail beyond restating the binary favorite action, so the baseline score of 3 is appropriate.

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 pair, "Mark or unmark," with a clear resource, "library posts as favorites," and clarifies the action's connection to the app's star feature. It is immediately distinguishable from all sibling tools, none of which cover favoriting posts.

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 provides clear context by linking the favorite state to list_viral_posts favorites_only filtering, which helps an agent understand the downstream effect of using this tool. It does not explicitly state when not to use it or name alternative tools, but the reference to the sibling list tool is enough to orient the agent.

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