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

Annotations only declare read-only and open-world, so the description carries the rest of the burden and does: it discloses the scoping precondition, the 100-item ceiling, that scores are historical snapshots, that an empty parent_id means top-level comments, and that timeouts/throttles surface as 503 with Retry-After. That is unusually complete behavioral context for a read tool.

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 scoping rule is front-loaded right after the purpose statement and every clause carries information (limits, error codes, alternative tool). It is a dense single paragraph of roughly 110 words, which is defensible for a 9-parameter tool but would read better broken into purpose / constraints / returns.

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?

Given 9 optional parameters, an output schema, and only safety annotations, the description covers everything needed to call it correctly: the mandatory scoping rule, time-bound behavior, result ceiling, error responses, and the sibling tool for a different shape of query. Return-value details are delegated to the output schema, which is appropriate.

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%, so the baseline is 3, but the description still adds value: it explains that query maps to Arctic Shift's body parameter (searching comment bodies, not titles), restates the sort default of desc, and clarifies the empty parent_id semantics. The parent_id clarification duplicates the schema text, which keeps this from a 5.

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 (Search) plus a specific resource (Arctic Shift's historical Reddit comment archive) and enumerates the five filter dimensions it supports. It also explicitly distinguishes itself from reddit_archive_comments_tree, so the agent can route between the two archive tools 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?

Gives explicit when-to-use and when-not-to-use guidance: a search must be scoped by author, subreddit, link_id, or parent_id, and time bounds can only narrow an already-scoped search. It names the sibling alternative (reddit_archive_comments_tree) and the condition that selects it (nested archived replies).

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