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

Annotations already declare readOnly, idempotent, open world, and non-destructive behavior, so the bar is lower. The description adds meaningful behavioral details beyond those: case-sensitive name resolution, approximate response size (about 5 KB), and the guarantee that no posts are included in the response.

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 efficiently structured: what it returns, why to use it, a critical behavioral caveat, and sibling routing. The field list is long but directly useful, and no sentence is wasted.

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 read-only metadata tool with an output schema, the description covers selection, invocation, caveats, and alternatives. Nothing material is missing: the agent knows what to expect, how to avoid case-sensitivity pitfalls, and when to choose a sibling tool instead.

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%, so the schema already documents both parameters, their examples, and the case-sensitivity requirement. The description adds that the tool works 'by name or by URL', which is useful context but largely reinforces what the schema already conveys.

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 names a specific verb ('Returns metadata') and a specific resource ('one subreddit'), and enumerates the exact fields returned. It also distinguishes itself from siblings by explicitly stating it returns no posts and pointing to get_reddit_subreddit and get_reddit_subreddit_search for those cases.

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?

It gives concrete use cases: 'size a community or read its rules before posting anything elsewhere.' It also states what the tool is not for ('returns no posts at all') and names the alternatives to use instead, giving an agent clear routing logic.

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