Deletes slack public/private channel messages, private chat messages and channel thread replies.

delete-slack-messages.js

#!/usr/bin/env node

// Channel ID is on the the browser URL.: https://mycompany.slack.com/messages/MYCHANNELID/
// Pass it as a parameter: node ./delete-slack-messages.js CHANNEL_ID

// CONFIGURATION #######################################################################################################

const token = 'SLACK TOKEN';
// Legacy tokens are no more supported.
// Please create an app or use an existing Slack App
// Add following scopes in your app from "OAuth & Permissions"
//  - channels:history
//  - groups:history
//  - im:history
//  - mpim:history
//  - chat:write

// VALIDATION ##########################################################################################################

if (token === 'SLACK TOKEN') {
    console.error('Token seems incorrect. Please open the file with an editor and modify the token variable.');
}

let channel = '';

if (process.argv[0].indexOf('node') !== -1 && process.argv.length > 2) {
    channel = process.argv[2];
} else if (process.argv.length > 1) {
    channel = process.argv[1];
} else {
    console.log('Usage: node ./delete-slack-messages.js CHANNEL_ID');
    process.exit(1);
}

// GLOBALS #############################################################################################################

const https         = require('https')
const historyApiUrl = `/api/conversations.history?channel=${channel}&count=1000&cursor=`;
const deleteApiUrl  = '/api/chat.delete';
const repliesApiUrl = `/api/conversations.replies?channel=${channel}&ts=`
let delay           = 300; // Delay between delete operations in milliseconds

// ---------------------------------------------------------------------------------------------------------------------

const sleep   = delay => new Promise(r => setTimeout(r, delay));
const request = (path, data) => new Promise((resolve, reject) => {

    const options = {
        hostname: 'slack.com',
        port    : 443,
        path    : path,
        method  : data ? 'POST' : 'GET',
        headers : {
            'Authorization': `Bearer ${token}`,
            'Content-Type' : 'application/json; charset=utf-8',
            'Accept'       : 'application/json'
        }
    };

    const req = https.request(options, res => {
        let body = '';

        res.on('data', chunk => (body += chunk));
        res.on('end', () => resolve(JSON.parse(body)));
    });

    req.on('error', reject);
    
    if (data) {
        req.write(JSON.stringify(data));
    }

    req.end();
});

// ---------------------------------------------------------------------------------------------------------------------

async function deleteMessages(threadTs, messages) {

    if (messages.length == 0) {
        return;
    }

    const message = messages.shift();

    if (message.thread_ts !== threadTs) {
        await fetchAndDeleteMessages(message.thread_ts, ''); // Fetching replies, it will delete main message as well.
    } else {
        const response = await request(deleteApiUrl, {channel: channel, ts: message.ts});

        if (response.ok === true) {
            console.log(message.ts + (threadTs ? ' reply' : '') + ' deleted!');
        } else if (response.ok === false) {
            console.log(message.ts + ' could not be deleted! (' + response.error + ')');

            if (response.error === 'ratelimited') {
                await sleep(1000);
                delay += 100; // If rate limited error caught then we need to increase delay.
                messages.unshift(message);
            }
        }
    }

    await sleep(delay);
    await deleteMessages(threadTs, messages);
}

// ---------------------------------------------------------------------------------------------------------------------

async function fetchAndDeleteMessages(threadTs, cursor) {

    const response = await request((threadTs ? repliesApiUrl + threadTs + '&cursor=' : historyApiUrl) + cursor);

    if (!response.ok) {
        console.error(response.error);
        return;
    }

    if (!response.messages || response.messages.length === 0) {
        return;
    }

    await deleteMessages(threadTs, response.messages);

    if (response.has_more) {
        await fetchAndDeleteMessages(threadTs, response.response_metadata.next_cursor);
    }
}

// ---------------------------------------------------------------------------------------------------------------------

fetchAndDeleteMessages(null, '');

then probably your token does not have enough permissons to delete it. Try to create a token with a more priviliged user.

yeah it should work in that case you can check the claims of the token.

Excellent script - thanks @firatkucuk !

@im-syk et al. - if anyone is interested in a version of this that deletes last 30 days, I made a version that does that. To change how long it keeps things for, update the keepTime variable as needed.

Thanks a lot, all work fine.