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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint=false, so safety is covered. The description adds genuinely new behavioral information: the credit cost model (1 credit + 1 per subreddit returned), which is not expressible in annotations. It omits failure behavior for nonexistent or banned subreddits, keeping it from a 5.

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?

Two short sentences with no filler: returned fields first, cost second. Front-loaded and appropriately sized, though the '1 credit per subreddit returned' phrasing is slightly redundant for a single-subreddit tool.

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?

A simple read-only lookup with a fully documented single parameter and no output schema; the description compensates by enumerating the returned fields and disclosing cost. Nothing critical an agent needs to call it correctly is missing, aside from error/nonexistent-subreddit behavior.

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 coverage is 100% and the schema itself documents the accepted formats (bare name, r/name, or URL) with an example. The description adds nothing about the name parameter, so the baseline of 3 is appropriate when the schema does all the work.

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?

States a specific resource (one subreddit) and verb (get metadata), and enumerates the returned fields: title, description, subscribers, over18, creation date. It does not explicitly differentiate from siblings like search_subreddits or get_subreddit_posts, but the singular 'one subreddit' framing makes the distinction inferable.

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?

Usage is implied by the singular scope — fetch metadata for a known subreddit rather than search for one — but no when/when-not conditions or named alternatives (e.g., 'use search_subreddits to find a name first') are given. An agent must infer the routing from the tool name alone.

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