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

Annotations already cover safety (readOnlyHint=true, destructiveHint=false, openWorldHint=true), so the bar is lower. The description adds genuinely non-structured behavior: 25 results per page, an enumerated return payload, and a per-page billing charge of $0.003 — cost and pagination are things an agent cannot see elsewhere.

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?

Three short sentences, each carrying distinct information: purpose, return shape, sibling routing + cost. The purpose is front-loaded and there is no filler.

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 no output schema, the description compensates by listing the returned fields, the page size, the cost per page, and the alternative tool for single-subreddit lookups. An agent has everything needed to call it correctly and to budget for it.

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% and both parameters (query, pages) are documented in the schema, including the 1-10 range and the 25-per-page mapping. The description only restates the 25-per-page fact already in the 'pages' parameter description, so it adds little beyond the schema — baseline 3.

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 verb+resource ('Search subreddits by keyword') and enumerates exactly what is returned, so an agent knows this returns subreddit entities rather than posts or users. It names reddit_subreddit_details as a different tool, but does not differentiate itself from the closest sibling, search_reddit (post search) or search_reddit_users.

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?

Explicitly routes the agent away for the single-subreddit case: 'Use reddit_subreddit_details for one subreddit's weekly activity.' That is a clear alternative with its condition. However, no guidance on when to prefer this over search_reddit or search_reddit_users, and no note on when the keyword search is the wrong tool.

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