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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the description is not needed to establish that this is a read-only open-world lookup. Still, the description adds useful context — duplicate removal, first-input ordering, missing ids reported, at most two upstream requests, an 8 MiB response cap, and credit costs with min/max. It does not describe the return format or pagination behavior. With annotations covering the safety profile, a 3 is appropriate.

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?

One dense paragraph, front-loaded with purpose and constraints, with no wasted sentences. Each clause conveys distinct operational value (cap, ordering, cost, alternatives).

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 an output schema present, return values needn't be explained, and the description covers all call-time concerns: id limits, batching, cost, and error recovery. Nothing an agent needs to invoke and retry correctly 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 100% and the single ids parameter is fully documented in the schema. The description adds behavioral detail (up to 1,000 ids, at most two 500-id requests) but not syntax or format beyond what the schema provides. Baseline 3 is correct when the schema does the heavy lifting.

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?

Specific verb (look up) plus resource (known Reddit post ids) plus scope (Arctic Shift's public historical archive). It explicitly points to the sibling search tool and to reddit_archive_comments_ids, so the agent can distinguish it from related 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?

Explicitly states the alternative path: use reddit_archive_posts_search to discover post ids and reddit_archive_comments_ids for archived comments. It also gives operational conditions (split large lookups and retry when the 8 MiB cap is hit).

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