Learn what works on your X account. And what to stop posting.

Crux, also called Cruxpost after its domain cruxpost.com, is a copilot for people who post on X (formerly Twitter). Instead of generating more posts, it measures what already works on your own account. You upload your X data archive or import your posts through X with read-only access, and Crux compares every post with the median of the 20 posts published nearest to it in time, so follower growth does not skew the result. It then reports which hooks, formats, topics and posting times do better or worse than usual for you, but only when a pattern holds across at least 5 posts and passes a significance test. On top of that measure, Radar counts posts on topics you track, Today scores each morning’s openings, and Crux drafts posts in your voice for you to publish yourself. Crux will cost $19 a month, one plan, after a 7-day free trial that needs no card. Billing is not open yet: during invite-only early access, approved accounts use Crux for free. Crux is not affiliated with X Corp.

Crux reports a pattern on your X account only when luck is unlikely to explain it. First comes a fair baseline: each post’s engagement (impressions where X provides them, otherwise likes plus 3 times reposts) is divided by the median of the 20 posts published nearest to it in time, giving a multiplier such as 2× your usual. Follower count barely moves across 20 consecutive posts, so early and recent posts stay comparable. Next, posts are grouped by hook, format, topic, weekday and time slot, and a group needs at least 5 posts. Then comes a permutation test: Crux draws the same number of your posts at random 500 times, takes each draw’s median multiplier, and keeps the 5th to 95th percentile as the range chance produces. A group above that range is reported as working for you, one below it as doing worse than usual, and anything inside it is not presented as a finding. If 35% or more of your posts got no engagement, Crux reports no patterns at all.

Crux tells you when to post on X from your own history, not from industry averages. Most “best time to post” charts pool posts from many other accounts, so they show when the average account does well, not when yours does. Crux groups your own posts by weekday and by 3-hour time slot, and measures each post against the median of the 20 posts you published nearest to it, which keeps an old post and a recent one on the same scale while your follower count changes. A slot is reported only when it holds at least 5 posts and its median result falls outside the range produced by 500 random draws of the same number of your posts: above it is a time that works for you, below it a time that does worse than usual. Slots that chance alone could explain are left out. Your Account DNA page names the time zone the slots are read in.

First download it: on X, open Settings and privacy, then Your account, then Download an archive of your data, confirm your password and request the archive. X sends an email and an in-app notification when it is ready. The archive is a .zip. Your posts are in data/tweets.js (large accounts also get tweets-part1.js and so on), long posts in note-tweet.js and account details in account.js. Each post carries its text, timestamp, likes and reposts as of the export, but no impressions: X leaves those out of archive downloads. Comparing raw likes across years misleads, because reach grows with your follower count. Crux handles this for you: upload the .zip (up to 500 MB) or just those files, and it scores each post against the 20 posts nearest it in time, then reports the hooks, formats, topics and posting times that do better or worse than usual for your account.

Crux is invite-only while it is in early access. Request access with the form on this page and include your X handle: approval is given to an X handle, and once your request is approved you sign in with that X account. Requests are read by hand. A request without a handle cannot be approved, because sign-in has nothing to match it to.

To sign in, read-only access through the X permissions tweet.read, users.read, offline.access. They let Crux read your posts and profile and stay connected without asking you to sign in again. Crux never asks for permission to like, follow or read direct messages. You can also upload your X archive instead of importing through X.

No. Crux never publishes, replies, likes or follows on your behalf, and signing in gives it read-only access. Anything you post, you post yourself on X.

For drafts and Radar topic ideas, when you ask for them, and for the short sentence under each of Today’s openings. Crux sends those requests to an AI model on Groq’s free plan. Other people’s posts are never sent to it, and the analysis of your posts and every score are computed in code, not by a model.

Crux will cost $19 a month, one plan, after a 7-day free trial that needs no card. Billing is not open yet: during invite-only early access, approved accounts use Crux for free.