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

Annotations only declare readOnly/openWorld; the description adds real behavioral substance: flattened-but-parentId-linked ordering, first-page-only scope, `raw.totalComments` as the full count, `pagination.hasMore` semantics, an explicit note that `pagination.cursor` is null, and a 1-credit cost. That is exactly the kind of information annotations cannot convey.

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?

Four tight sentences, zero filler, with the core behavior front-loaded and the routing/cost details trailing. Every clause (ordering, parentId, first-page scope, cursor null, credit cost) carries information the agent needs.

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?

No output schema exists, and the description fully covers the return contract (comment tree shape, parent linking, total count field, pagination flags) plus the partial-retrieval caveat and its remedy. Nothing an agent needs to call or interpret results is missing.

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 80%: `url`, `sort`, `depth`, and `limit` are documented inline, so the baseline is 3. The description adds no meaning about `depth` or `limit` beyond the schema, and `cache_max_age` is undocumented in both places, so there's no compensation to justify higher.

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 ('Post comments. A post's comment tree, flattened into reading order') and immediately distinguishes the shape of the result with `parentId` preserved. It also names the sibling (reddit_commentReplies) that handles the case this tool does not, so an agent can disambiguate 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?

Explicitly routes deep-thread continuation stubs to `reddit.commentReplies`, which is a concrete when-to-use-something-else rule. It doesn't mention prerequisites (e.g., that a post URL/id is needed vs. reddit_post for post metadata), but the context is clear enough to act on.

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