Discord webhook rate limits

Question

I'm working on a private browser extension which extracts some information from a web page and posts it into a Discord channel via a webhook.

The browser extension does evaluate the x-ratelimit-... response headers to observe the rate limit restrictions.

While doing a "spam test" it seems that the rate limit restrictions are respected correctly and everything is working so far. However, every now and then I'm still getting rate limited after sending a stack of messages (15+) even though ratelimit-remaining is > 0.

To counter this I already stop when ratelimit-remaining is 1 and also add an additional second to the ratelimit-reset timestamp. But this doesn't seem to help.

let rateLimitRemaining = 5;
let rateLimitReset = 0;

function sendContent()
{
    if ( contentQueue.length > 0 )
    {
        console.log( "Messages in content queue: " + contentQueue.length );

        let content = contentQueue[ 0 ];
        let dateTimestamp = getCurrentUTCTimestamp();

        // Don't send if remaining rate limit is <= 1 and current UTC time is less than reset timestamp
        if ( rateLimitRemaining <= 1 && dateTimestamp <= rateLimitReset )
            return;

        contentQueue.shift();

        let url = "...";
        sendMessage( content, url );
    }
}

function sendMessage( content, url )
{
    let payload = JSON.stringify( { "content": content } );
    $.ajax(
    {
        contentType: 'application/json',
        method: "POST",
        url: url,
        data: payload,
        dataType: 'json'
    } ).done( function( response, status, jqXHR )
    {
        rateLimitRemaining = parseInt( jqXHR.getResponseHeader( 'x-ratelimit-remaining' ) );
        // Add an additional second to the reset timestamp
        rateLimitReset = parseInt( jqXHR.getResponseHeader( 'x-ratelimit-reset' ) ) + 1;

        let timeToResetRemaining = rateLimitReset - getCurrentUTCTimestamp();
        console.log( '[' + getCurrentDateTime() + '] Content sent to webhook. Remaining until rate limit: ' + rateLimitRemaining + ' / Reset @ ' + rateLimitReset + ' (' + getCurrentUTCTimestamp() + ') (' + timeToResetRemaining + ')' );
    } ).fail( function( jqXHR, status, error )
    {
        let response = jqXHR.responseJSON;

        // If we got rate limited, respect the retry_after delay
        if ( response.hasOwnProperty( 'message' ) && response.message.indexOf( 'rate limited' ) !== 0 )
        {
            rateLimitRemaining = 0;
            rateLimitReset = getCurrentUTCTimestamp() + Math.ceil( response.retry_after / 1000 ) + 1;
        }

        console.log( '[' + getCurrentDateTime() + '] Error sending request to webhook.' );
        console.log( response );
    } );
}

It is also strange that the same request, which triggers the rate limit, has its x-ratelimit-remaining response header at > 0.

What do I miss here? Where is my mistake? Do I need to take x-ratelimit-bucket and x-ratelimit-reset-after into account aswell?

Answer 1

A webhook that does not send a bot token is limited by a different set of rate limits to other API calls.

Each channel has a rate limit of maximum number of webhook messages that can be sent per minute, this limit is shared amongst all senders, so other bots and services might impact your ability to deliver a webhook. This limit is 30 messages per minute currently and not documented. Previously discord developers have tweeted this limit exists; https://twitter.com/lolpython/status/967621046277820416

The second limit is per IP, which you can monitor yourself and prevent any 429's from this. You will have to monitor the headers returned from the request to manage this.

on top of this, there is a final limit of 50 requests per second per IP; https://blog.xenon.bot/handling-rate-limits-at-scale-fb7b453cb235 - this is enforced at cloudflare.

Let me know if you have any more questions!