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

Annotations only declare readOnlyHint and openWorldHint. The description adds real operational context: 503 with a Retry-After header means throttling, waiting that many seconds before retry, and that native-source failures fall back to an internal Redlib source whose public fields and credit weights are preserved. This is meaningful behavior an agent needs and that no structured field carries.

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?

Purpose is front-loaded, then error handling, then fallback, then the alternative. The parameter sentence is interleaved awkwardly between the operational notes and the sibling routing, which slightly breaks flow, but every sentence carries information and there is no padding.

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?

With a 100%-covered schema and an output schema present, the description does not need to explain return fields, and it correctly avoids doing so while still characterizing the payload ('flat public comment entries'). For a read-only paginated feed tool it covers what an agent needs: purpose, error/retry handling, fallback behavior, and the sibling to use 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 username, after, and limit are already documented in the schema. The description's 'username: Public Reddit username. Required.' merely restates the schema and adds no meaning for after/limit or the cursor format, so the baseline 3 applies.

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 first sentence states a specific verb (Returns), resource (comment entries), and scope (flat, public, a Reddit user's comments feed). It also explicitly names the sibling it is not ('Use reddit_comments to get Reddit post comments'), so an agent can distinguish it from reddit_comments and reddit_subreddit_comments without opening a schema.

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 a clear when-not: use reddit_comments for post comments, routing the agent to the correct alternative. It also describes the retry path for 503s. However, it never states the positive trigger for choosing this tool over reddit_user_posts or search, so usage context is clear but not exhaustive.

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