Emacs Lisp Reddit API Wrapper

A couple of months ago I wrote an Emacs Lisp wrapper for the reddit API. I didn’t put it in MELPA, not yet anyway. If anyone is finding it useful I’ll see about getting that done. My intention was give it some exercise and testing before putting it out there for people to use, locking down the API. You can find it here,

Except for logging in, the library is agnostic about the actual API endpoints themselves. It just knows how to translate between Elisp and the reddit API protocol. This makes the library dead simple to use. I had considered supporting OAuth2 authentication rather than password authentication, but reddit’s OAuth2 support is pretty rough around the edges.

Library Usage

The reddit API has two kinds of endpoints, GET and POST, so there are really only three functions to concern yourself with.

And one variable,

The reddit-login function is really just a special case of reddit-post. It returns a session value (cookie/modhash tuple) that is used by the other two functions for authenticating the user. Just as you get automatically with almost all Elisp data structures — probably more so than any other popular programming language — it can be serialized with the printer and reader, allowing a reddit session to be maintained across Emacs sessions.

The return value of reddit-login generally doesn’t need to be captured. It automatically sets the dynamic variable reddit-session, which is what the other functions access for authentication. This can be bound with let to other session values in order to switch between different users.

Both reddit-get and reddit-post take an endpoint name and a list of key-value pairs in the form of a property list (plist). (The api-type key is automatically supplied.) They each return the JSON response from the server in association list (alist) form. The actual shape of this data matches the response from reddit, which, unfortunately, is inconsistent and unspecified, so writing any sort of program to operate on the API requires lots of trial and error. If the API responded with an error, these functions signal a reddit-error.

Typical usage looks like so. Notice that values need not be only strings; they just need to print to something reasonable.

;; Login first
(reddit-login "your-username" "your-password")

;; Subscribe to a subreddit
(reddit-post "/api/subscribe" '(:sr "t5_2s49f" :action sub))

;; Post a comment
(reddit-post "/api/comment/" '(:text "Hello world." :thing_id "t1_cd3ar7y"))

For plists keys I considered automatically converting between dashes and underscores so that the keywords could have Lisp-style names. But the reddit API is inconsistent, using both, so there’s no correct way to do this.

To further refine the API it might be worth defining a function for each of the reddit endpoints, forming a facade for the wrapper library, hiding way the plist arguments and complicated responses. That would eliminate the trial and error of using the API.

(defun reddit-api-comment (parent comment)
  (if (null reddit-session)
      (error "Not logged in.")
    ;; TODO: reduce the return value into a thing/struct
    (reddit-post "/api/comment/" '(:thing_id parent :text comment))))

Furthermore there could be defstructs for comments, posts, subreddits, etc. so that the “thing” ID stuff is hidden away. This is basically what was already done for sessions out of necessity. I might add these structs and functions someday but I don’t currently have a need for it.

It would be neat to use this API to create an interface to reddit from within Emacs. I imagine it might look like one of the Emacs mail clients, or like Elfeed. Almost everything, including viewing image posts within Emacs, should be possible.


For the last 3.5 years I’ve been a moderator of /r/civ, starting back when it had about 100 subscribers. As of this writing it’s just short of 60k subscribers and we’re now up to 9 moderators.

A few months ago we decided to institute a self-post-only Sunday. All day Sunday, midnight to midnight Eastern time, only self-posts are allowed in the subreddit. One of the other moderators was turning this on and off manually, so I offered to write a bot to do the job. There weren’t any Lisp wrappers yet (though raw4j could be used with Clojure), so I decided to write one.

As mentioned before, the reddit API leaves a lot to be desired. It randomly returns errors, so a correct program needs to be prepared to retry requests after a short delay, depending on the error. My particular annoyance is that the /api/site_admin endpoint requires that most of its keys are supplied, and it’s not documented which ones are required. Even worse, there’s no single endpoint to get all of the required values, the key names between endpoints are inconsistent, and even the values themselves can’t be returned as-is, requiring massaging/fixing before returning them back to the API.

I hope other people find this library useful!

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Chris Wellons

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