Trigger: NUI, ui_page, SendNUIMessage, SetNUIFocus, RegisterNUICallback, HTML/CSS/JS for FiveM, FiveM menu UI. Build FiveM NUI pages, wire Lua-browser messaging, callbacks and focus.

FiveM NUI HTML/CSS/JS interfaces for FiveM: manifest setup, Lua to browser messages, NUI callbacks and focus handling. Activation Contract Load this skill when the user asks to create or edit a FiveM UI, writes HTML/CSS/JS inside a resource, sets ui page , or asks about SendNUIMessage , SetNUIFocus or RegisterNUICallback . Hard Rules Declare ui page and include every UI file in files in fxmanifest.lua ; a missing file silently fails to load. Reference assets with https://cfx nui <resource /path ; the nui:// protocol is deprecated. RegisterNUICallback handlers must ALWAYS call cb(...) (at least cb({}) ), or the browser request hangs. Browser calls callbacks with fetch('https://' + GetParentResourceName() + '/<name ', { method: 'POST', body: JSON.stringify(...) }) ; the URL name must match the registered name exactly. SetNUIFocus(keyboard, mouse) : always call SetNUIFocus(false, false) when closing the UI. NUI callbacks run on the CLIENT. Validate their data client side, then re validate on the server before any state change; never trust UI sent prices, amounts or ids. Minimize SendNUIMessage calls: batch updates rather than sending per frame. Debug with F8 and Chrome DevTools; test the page in a browser with a mock mode. Decision Gates Direction Mechanism Lua to browser SendNUIMessage({ type = ..., data = ... }) + window.addEventListener('message') Browser to Lua fetch POST to https://<resource /<callback + RegisterNUICallback Browser wants server data callback to Lua client, then a server callback Show / hide cursor SetNUIFocus(true, true) / SetNUIFocus(false, false) Keyboard only SetNUIFocus(true, false) Execution Steps 1. Add ui page and files to the manifest (read rules/setup.md). 2. Build index.html , CSS and JS; listen for message events keyed by type . 3. Register Lua callbacks for every action the UI can request; call cb on every path. 4. Manage focus on open/close; handle Escape to close. 5. Forward any state changing action to the server and validate there. Output Contract Return the manifest entries, the HTML/CSS/JS files, and the Lua client script with callbacks and focus handling. Keep security relevant logic on the server. References rules/setup.md — folder layout, manifest, build tools, common mistakes. rules/fullscreen nui.md — SendNUIMessage, SetNUIFocus, focus stack, assets, devtools. rules/nui callbacks.md — RegisterNUICallback, fetch, async, errors, security. rules/best practices.md — performance, security, state, error handling, testing. rules/reference links.md — official docs and natives reference. Upstream docs: https://docs.fivem.net/docs/scripting manual/nui development/

fivem-nui