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

Annotations already declare readOnly/idempotent/openWorld, so the bar is lower, yet the description adds substantive context: archive depth back to ~2005, the live API's ~1,000-result ceiling with no reliable date filter, the returned fields, and error behavior (unindexed subreddit yields a loud error, never a silent empty list). That last point prevents a costly misinterpretation of empty results.

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?

Scope and source are front-loaded, followed by the routing rule, then the parameters, then the failure mode. It is dense but every sentence carries distinct information — 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?

No output schema exists, and the description compensates by listing returned fields (id, title, author, created_utc ISO, score, num_comments, permalink) and documenting failure behavior and archive coverage. An agent has everything needed to call it and interpret results.

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 field-level meaning is already documented. The description still adds the combination semantics — date range and keyword can be applied 'and/or' — which the schema does not state, plus the ISO date example format used in practice.

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 and its scope: historical Reddit POSTS from one subreddit, sourced from the Arctic Shift archive rather than the live Reddit API. It explicitly distinguishes itself from the live `reddit` pack, so an agent can route correctly without inspecting the 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 PREFER conditions ("Reddit posts about X in/before <year>", "what did r/<sub> post about Y historically") and names the excluded case — anything the live reddit pack can date-filter. The alternative and the selecting condition are both stated.

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