The AI that
compiles what it writes
Lexi is the assistant built into the letX editor. It reads your whole project, meaning every file, your bibliography and the compile log, then edits the source in place and rebuilds the PDF. So when something fails it fixes the line LaTeX actually complained about, instead of guessing at code you then have to paste somewhere and try yourself.
Why “it can compile” is the whole difference
Every general-purpose AI writes LaTeX. None of them can tell whether the LaTeX they wrote builds. That gap is where the time goes: you paste, it fails, you copy the error back, it apologises and guesses again. A missing package, a stray ampersand in an aligned environment, a figure path that is right on your machine and wrong on the server. None of those are visible to something that never ran the build.
Lexi runs it. It gets the real log back, finds the line the error points at, changes that line, and compiles again. That is the loop you would run by hand, without the copying.
Eighteen things it does on request
Type / in the Lexi panel, or press Cmd-K on a selection to edit just that passage.
/fixReads the compile log, finds the error LaTeX actually reported, and fixes it in the file.
/tableTurns pasted numbers into a booktabs table that compiles.
/diagramDraws a TikZ diagram from a description.
/image-to-texRecreates a screenshot of a table, equation, or layout as LaTeX.
/pdf-to-texRebuilds a PDF document, form, or deck as an editable LaTeX source.
/slidesTurns a paper into a Beamer deck.
/convertReformats a document for another venue, such as IEEE to Springer or article to thesis.
/formatFixes spacing, sectioning, and layout without touching your words.
/citeAdds a citation and the matching .bib entry.
/shortenCuts text to a word or page limit without losing the argument.
/humanizeRewrites a passage to read in your voice instead of house-style AI prose.
/cleanStrips invisible characters and normalises punctuation. It knows where the maths is, so equations survive.
/translateTranslates text and sets up the fonts the script needs.
/explainExplains a command or an error in plain language.
/outlineProposes a structure for a document that does not have one yet.
/scaffoldGenerates a starter document for a kind of writing.
/beamerGenerates a starter talk.
/figureInserts a figure with the float, caption, and label wired up.
Or bring your own assistant
If you already work in Claude or ChatGPT, you do not have to move. letX runs an MCP server that hands those assistants the same abilities: search the template library, create a project, edit its files, compile it to PDF. Same compile farm, same version history, different chat window.
Questions
What is Lexi?
Lexi is the AI assistant built into the letX LaTeX editor. It reads the project you have open, meaning every file, the bibliography and the compile log, then edits the source directly and recompiles. The changes land in the document rather than in a chat window you copy from, and every one of them can be undone from letX version history.
How is that different from asking ChatGPT for LaTeX?
A general chat assistant cannot compile. It writes plausible LaTeX, you paste it, it fails, and you copy the error back. Lexi runs the build, reads the real latexmk log, and fixes the line LaTeX complained about. The loop closes inside the editor. If you would rather stay in ChatGPT or Claude, the letX MCP server gives them the same compile access.
Does Lexi change my document without asking?
Edits are applied to the open document so you can see them, and the version before each edit is kept in history, one click away. Inline Cmd-K edits act on the selection you made and nothing else.
Is Lexi free?
Lexi is a Pro feature with a usage allowance. The editor itself, the 1000+ template library, real-time collaboration, and unlimited compiling are free.
Is my writing used to train AI?
No. Your documents are not used to train models without your consent. That is the same commitment across all of letX, and it is why a lot of research groups pick it over an AI-first editor.
Can Lexi work in languages other than English?
Yes. /translate handles the text, and letX sets up the packages and fonts the script needs, including Arabic, Hebrew, CJK and Indic scripts, then switches the project to an engine that can typeset them.