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by redditapis
OverviewSchemaSourceRelated ServersDiscussionsAdmin
JavaScript
Remote

reddit_search_communities

Read-only

Find subreddits by name or topic, returning titles, subscriber counts, descriptions, and NSFW flags. Discover where a topic is discussed before searching its posts.

Instructions

Search for subreddits (communities) by name or topic. Returns matching subreddits with title, subscriber count, description, and NSFW flag. Use to discover where a topic is discussed before listing or searching its posts. Example: q='machine learning'.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
qYesSearch query text. Supports Reddit search syntax (e.g. `subreddit:webdev`, `author:spez`, `"exact phrase"`, `title:...`).
nsfwNoSet 'true' to include over-18 / NSFW results. Omit or 'false' to exclude them (default).
afterNoOpaque pagination cursor. Pass back the previous response's `after` value EXACTLY as it was returned; the format is not stable and a hand-written Reddit fullname loses the paging depth the cursor carries. Omit on the first call. When `after` comes back null there is no next page to request, and that does NOT reliably mean you have every item: Reddit often stops serving a busy listing long before it runs out. Read `listing_status` on that final response instead. It is `complete`, `truncated` or `unknown`, and ONLY `complete` means nothing is missing. Never report `truncated` or `unknown` to a user as the end of the data; say the answer is partial and widen across sorts, timeframes or search terms.
limitNoMax items to return (1 to 100). The API clamps out-of-range values; endpoint default applies if omitted.

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed1 schema field changedv0.5.3
    • changedInput schema / properties / after / description
      Previous value: -"Opaque Reddit pagination cursor from the previous response's `after` field (a fullname like `t3_abc123`). Omit on the first call; pass it to fetch the next page."New value: +"Opaque pagination cursor. Pass back the previous response's `after` value EXACTLY as it was returned; the format is not stable and a hand-written Reddit fullname loses the paging depth the cursor carries. Omit on the first call. When `after` comes back null there is no next page to request, and that does NOT reliably mean you have every item: Reddit often stops serving a busy listing long before it runs out. Read `listing_status` on that final response instead. It is `complete`, `truncated` or `unknown`, and ONLY `complete` means nothing is missing. Never report `truncated` or `unknown` to a user as the end of the data; say the answer is partial and widen across sorts, timeframes or search terms."
  2. First observedv0.1.12

TDQS

A4/5.0
Behavior3/5

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

Annotations already declare readOnlyHint=true, openWorldHint=true and destructiveHint=false, so safety is covered. The description adds the return payload shape (title, subscriber count, description, NSFW flag), but says nothing about rate limits, auth requirements, or the truncation/pagination caveats that the schema's `after` param carries.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Three short sentences, front-loaded with purpose, then return shape, then usage, then a one-line example. No sentence is redundant and nothing is buried.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

With no output schema, the description usefully enumerates the returned fields, and the safety profile is covered by annotations while pagination/truncation behavior lives in the schema. It does not mention the `limit`/paging model at all, which is the one detail an agent might want summarized in prose.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so all four parameters are already documented in detail, including the enum for `nsfw` and the extensive `after` cursor semantics. The description only adds an illustrative q value, so the baseline of 3 applies.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb and resource ('Search for subreddits (communities) by name or topic') and disambiguates it from post-oriented siblings by naming the returned fields and positioning it as a discovery step before listing or searching posts. The example query makes the operation concrete.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Gives clear situational guidance ('Use to discover where a topic is discussed before listing or searching its posts') that tells the agent when this tool is the right entry point versus post search. It stops short of naming explicit alternatives or stating when NOT to use it, so it is clear context rather than full routing logic.

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

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