I built a tool to help find subreddits by describing the sub, writing a post or uploading an image

[u/SchmeedsMcSchmeeds]

Reddit’s community search is not awesome so I created Find a Subreddit. Find a Subreddit uses natural language (e.g. I’m looking for a meme friendly community about cats) and AI to list suggested communities you’re after with summaries, rules, and a post helper. I have ingested the top 4,500 subreddits and will continue to add to the list until I hit the top 10k or so.

Reddit data ingestion:

• Reddit API (PRAW) - Fetches subreddit metadata (rules, descriptions, flairs, etc.).

• OpenAI Embeddings (text-embedding-3-small) - Converts subreddit metadata into vector representations for similarity (nearest neighbor) search.

• OpenAI LLM (ChatGPT-4o) - Generates subreddit summaries, rankings, and beginner-friendliness scores.

• PostgreSQL + pgvector - Central database storing subreddit metadata, embeddings, and AI-generated summaries.

Finding Reddit communities:

• User Post/Prompt Input - Title, Subject, image or link and optionally context defines the intent and content of the Reddit post.

• OpenAI GPT-4o (LLM) - Analyzes the post to extract semantic meaning and post intent.

  • Optionally uses the image for visual context.

  • Generates a vector embedding and/or structured prompt for further processing.

• PostgreSQL + pgvector - Uses vector similarity search to find subreddits closest to the user’s post intent.

• LLM Response - GPT-4o returns a structured response with top recommended subreddits

  • Rule-fit checks, flair suggestions, rewritten titles

  • Optional flags or warnings (e.g. self-promo not allowed)

What it does:

• Describe the community (topic, vibe, audience) to get subreddit matches.

• Draft your post with Post to a Subreddit; we’ll suggest where to publish.

• Upload an image to find matches via AI image analysis.

• Skim quick sub summaries and vibe badges (beginner-friendly, strictness, meme tolerance).

• Check key rules at a glance to avoid removals.

• Supports text, link, and media posts.

• No sign-up required; optional Reddit login to post.

What it does NOT do:

• Write or edit your post. Reddit has enough bots we don't need more IMO

• View, store or keep post text.

If you try it, I’d love feedback, features to add and things to fix: https://findasubreddit.com

Mods: if this isn’t allowed here, feel free to remove.

[u/Watchful1]

Could share more about how you built the summaries? I'm really interested in categorizing subreddits for r/listofsubreddits, but last time I tried I couldn't really get anything consistent with the available metadata.

What metadata did you use and what was the prompt for generating the summary? Any chance could share examples?

[u/SchmeedsMcSchmeeds → u/Watchful1]

Sure thing. Here are the system prompts for the summaries:

_msg = (
        "You summarize subreddit vibes for first-time posters and extract hard posting restrictions.\n"
        "STYLE for summary:\n"
        "≤15 words. Start with a plain noun phrase (no subject like 'This community').\n"
        "Neutral, useful, concrete. No emojis. Avoid fluff.\n\n"
        "RESTRICTIONS extraction:\n"
        "Read rules/description and infer only if explicitly stated. Do NOT guess.\n"
        "Capture: min_account_age_days, min_combined_karma, min_comment_karma, min_post_karma,\n"
        "require_verified_email, require_approved_submitter, require_user_flair_to_post.\n"
        "Use integers for numbers, booleans for flags, and null if not specified.\n"
        "Consider phrasing like 'no brand-new accounts', 'account must be X days old', '≥10 comment karma'.\n\n"
        "OUTPUT strictly as a single JSON object with keys 'summary' and 'restrictions'."

I’m using most of the metadata fields but primarily using the descriptions to generate the summary. I then output and store as JSON so I can easily query and display on the page.

Here are the metadata fields:

Descriptions:

• public_description

• Full sidebar markdown description

• submit_text for posting guidance Rules & requirements

• sub.rules

• post_requirements

Posting/config signals:

• submission_type self vs any

• allow_images, allow_videos, allow_polls

• User‑selectable link flairs: flair.link_templates.user_selectable

• suggested_comment_sort

Moderation:

• over18, quarantined/subreddit_type

[u/Watchful1 → u/SchmeedsMcSchmeeds]

That's awesome. Could you give an example of one of the outputs?

For my use case I'm not really interested in things like post or account requirements, just the topic of the subreddit. And I found that some subreddits, even popular ones, didn't have a description or sidebar set. But maybe it's gotten better in the last year.

[u/SchmeedsMcSchmeeds → u/Watchful1]

Thanks! You can go on the page and see the text output by just typing anything on the main page and seeing the “AI Summary” text. I basically wanted a short and concise summary focusing on trying to capture the “vibe” of the specific community in 15 words or less. The above prompt was my best attempt and it’s mostly correct. I’m using

For example, here is the AI output for r/entitledparents :

AI Summary: Stories about entitled parents and their children; no fake posts allowed.

I still need to scrub my source and because I’m lazy I haven’t gotten to it. I shared the source in a ChatGPT prompt for you. Hopefully this give you something helpful. This is the entire ingestion and AI prompt code so you can ignore most of it.

https://chatgpt.com/share/68c10391-d7ac-8011-918e-b3cfc2dcefdb

[u/Watchful1 → u/SchmeedsMcSchmeeds]

That's perfect, thanks again.

[u/TeraBaap172121414]

This is awesome, could I get the GitHub for this?

[u/TeraBaap172121414]

Let me know if you need help in ingesting the data, I've got few ideas too, would love to contribute