Reddit Subreddit Finder & Ranker

Give it a topic and it hands back the communities worth posting in — ranked by how alive they actually are, not by how many people once clicked "join". For every topic it merges three independent discovery sources, deduplicates the results, filters out user profiles, private communities and anything outside your size window, then samples each survivor's recent posts to measure real posting cadence, median score, median comments and engagement per subscriber. That last number is what separates the 40,000-member community where your post gets read from the 4,000,000-member one where it sinks in eleven minutes. Built for marketers, community managers, founders, researchers and anyone tired of guessing which subreddit is the right one.

What you can do with it

• Find where your audience already is. Feed in your product category and get a ranked list of the communities discussing it, including the niche ones that never show up in Reddit's own search box.
• Avoid the graveyards. Subscriber counts include everyone who ever joined, including people who left Reddit in 2016. Posts per day and median comments tell you whether anyone is still home.
• Pick the community where you will actually be seen. The opportunity score ranks by engagement per subscriber, so under-saturated communities rise to the top instead of the giants everyone already posts in.
• Build a Reddit posting calendar. Export the shortlist, sort by activity level, and plan which community gets which piece of content.
• Size up a niche before you enter it. Total members, total daily engagement and author diversity across every community for a topic tell you how big and how concentrated the conversation really is.
• Research competitors' territory. Search their product name as a topic and see every community where it comes up.

What you get

One row per subreddit. Abridged real example:

{
  "rank": 1,
  "name": "homeassistant",
  "title": "Home Assistant",
  "url": "https://www.reddit.com/r/homeassistant/",
  "subscribers": 574660,
  "description": "Open source home automation that puts local control and privacy first. Powered by a worldwide community of tinkerers and DIY enthusiasts.",
  "createdAt": "2015-12-19T13:02:23.000Z",
  "subredditType": "public",
  "over18": false,
  "language": "en",
  "submissionType": "any",
  "allowsImages": true,
  "allowsPolls": true,
  "matchedTopics": ["home automation"],
  "matchedTopicCount": 1,
  "discoveredVia": ["subreddit-search", "autocomplete", "post-search"],
  "sourceCount": 3,
  "activityAnalyzed": true,
  "sampleSize": 50,
  "sampleOldestPostAt": "2026-07-28T04:39:57.000Z",
  "sampleNewestPostAt": "2026-07-28T20:56:40.000Z",
  "sampleSpanHours": 16.28,
  "newestPostAgeHours": 0.05,
  "postsPerDay": 72.242,
  "engagementSampleSize": 30,
  "engagementIsProvisional": false,
  "medianScore": 2,
  "medianComments": 4.5,
  "averageScore": 28.43,
  "commentsPerPost": 24,
  "distinctAuthors": 49,
  "authorDiversity": 0.98,
  "activityLevel": "very-high",
  "engagementPerPost": 11,
  "dailyEngagement": 794.66,
  "engagementPer1kSubscribers": 1.3828,
  "opportunityScore": 13.97,
  "scrapedAt": "2026-07-28T20:59:42.015Z"
}

That is a real row: r/homeassistant was returned by all three discovery sources for the topic "home automation", posts 72 times a day, and outranks the 4.5-million-member r/homeautomation because its audience is far more engaged per member.

Input reference

Field	Type	Default	What it does
topics	list of text	— (required)	The topics, niches, products or keywords to find communities for, one per line. Plain phrases work best: home automation, indie game marketing, mechanical keyboards. Each topic is searched separately and the results are merged.
minSubscribers	number	1000	Skip communities smaller than this. Filters out abandoned and one-person communities while keeping genuinely niche ones.
maxSubscribers	number	none	Skip communities larger than this. Use it to deliberately avoid the huge default subreddits.
includeNsfw	true/false	false	Keep adult and quarantined communities in the results.
maxSubredditsPerTopic	number	50	How many communities to keep per topic after filtering. The strongest matches are kept: found by several sources, ranked highly by Reddit's own relevance order. Maximum 500.
analyzeActivity	true/false	true	Read a sample of each community's recent posts to compute cadence, medians and the opportunity score. Turn off for a faster, cheaper discovery-only run.
activitySampleSize	number	50	How many recent posts to read per community. 10–500.
maxConcurrency	number	5	How many communities to work on at once. 1–20.
country	select	us	Which country's view of Reddit to use.

Output fields

Field	Type	Description
rank	number	Position in the final ranking, 1 = best opportunity.
name	text	Subreddit name, without the r/.
title	text	The community's own headline.
url	link	Direct link to the subreddit.
subscribers	number	Total members.
description	text	The community's public description.
createdAt	date	When the community was created.
subredditType	text	public or restricted.
over18 / quarantined	true/false	Adult and quarantine flags. Empty on the rare row whose community flag could not be read — never guessed as false.
language, category	text	Community language and Reddit's own category.
icon, banner	link	Community artwork.
submissionType	text	What can be posted: any, self or link.
allowsImages, allowsVideos, allowsPolls, wikiEnabled	true/false	Community features.
matchedTopics	list	Which of your topics found this community.
matchedTopicCount	number	How many of your topics it matched.
discoveredVia	list	Which discovery sources returned it.
sourceCount	number	How many of the three sources agreed — a relevance signal in itself.
activityAnalyzed	true/false	Whether a post sample was measured for this row.
sampleSize	number	How many recent posts were measured.
sampleOldestPostAt, sampleNewestPostAt	date	The window the sample covers.
sampleSpanHours	number	How many hours that window spans.
newestPostAgeHours	number	How long ago the most recent post appeared.
postsPerDay	number	Real posting cadence measured across the sample.
engagementSampleSize	number	How many posts the score and comment medians were counted from — the settled posts, or the whole sample when too few of them had settled (see below).
engagementIsProvisional	true/false	True when the community posts so fast that fewer than three of its sampled posts have settled. The medians then cover the whole sample and are a floor rather than a settled figure.
medianScore	number	Median upvote score across the counted posts.
medianComments	number	Median comment count across the counted posts.
averageScore	number	Mean score — compare with the median to spot outlier-driven communities.
commentsPerPost	number	Mean comments per post.
distinctAuthors	number	How many different people posted in the sample.
authorDiversity	number	Distinct authors ÷ sample size. Low means a handful of people carry the community.
activityLevel	text	very-high, high, moderate, low, dormant, or unknown when the sample was too thin to measure a cadence.
engagementPerPost	number	Median score plus twice the median comments.
dailyEngagement	number	Engagement per post × posts per day.
engagementPer1kSubscribers	number	Daily engagement per 1,000 members — the raw signal behind the score.
opportunityScore	number	0–100. Engagement per subscriber on a logarithmic curve. High = an active audience that is not yet saturated.
scrapedAt	date	When the row was produced.

Rows are ordered by opportunityScore, highest first, with ties broken by member count. If you would rather rank by raw reach, sort by subscribers — both numbers are in every row.

How activity is measured. The sample is read from the community's most recent posts. Posting cadence uses every post in it, but score and comment medians deliberately ignore posts less than six hours old: a post that went up four minutes ago has a score of 1 no matter how good the community is, and the busier the community the younger its newest posts are — scoring those would punish a community for being active. engagementSampleSize tells you how many posts actually counted. In the rare case where fewer than three of them have settled, the medians fall back to the whole sample and engagementIsProvisional is set so you know to read them as a floor. Pinned announcements are left out of both the cadence and the medians — they sit at the top of a community forever and would distort each.

Pricing

Pay per event, so you pay for results rather than for runtime.

What you pay for	Price	Effective rate
Ranked subreddit — one row written to your dataset	$0.001	$1.00 per 1,000 communities
subreddit-activity-analysis — one community measured for cadence, medians and the opportunity score	$0.002	$0.002 per community measured

Communities filtered out by your subscriber range or NSFW setting are never charged, and duplicates across topics are merged into one row before anything is billed. The activity charge only applies to communities that were actually measured: turn analyzeActivity off and it never applies at all, and a community that could not be measured is not charged for it.

FAQ

Do I need a Reddit account? No. You do not need a Reddit account, a login, or any credentials — just enter what you want and run it.

What does it cover? Everything Reddit shows the public. Communities that are private or banned are not included.

How fast is it? Results come back in large batches, so big jobs finish in minutes rather than hours. A typical run — three topics, 50 communities each, activity measured — is a few minutes end to end. Raise maxConcurrency to go faster.

How many communities will one topic return? Up to maxSubredditsPerTopic (50 by default, 500 maximum) after filtering. Broad topics comfortably fill that; very narrow ones return fewer, which is itself useful information.

Why is a community with fewer members ranked above a bigger one? That is the point. The ranking is engagement per subscriber, so a busy 30,000 member community outranks a sleepy 3,000,000 member one. Sort by subscribers if you want the reach ranking instead.

Can I run it on a schedule? Yes. Communities and their activity shift over time, so a monthly or quarterly run keeps your shortlist current. Each run returns the full current picture — there is no state carried between runs.

Does it return NSFW communities? Only if you switch includeNsfw on. Adult and quarantined communities are excluded by default, and so is the occasional community whose adult flag could not be read at all — an unknown is never treated as safe.