Lua for FiveM: the basics, common mistakes and the AI skill

Lua for FiveM is a small language with a few sharp edges, and most broken resources trip on those edges rather than on the FiveM API. Arrays start at 1, nil and false are different, there is no continue and no ternary. If you write or review Lua resources, or you let an AI assistant write them for you, you need these rules in front of you. The Lua basics skill packs them into rule files the assistant reads before writing code.

What the Lua basics skill gives you

The SKILL.md is an index. Each topic has its own rule file with explanations and examples.

• rules/functions.md. Function size, naming, parameters, exports and guard clauses. Short functions that return early instead of nesting.
• rules/tables.md. Array indices start at 1, dereferencing, avoiding table.insert in hot paths, iteration with ipairs and pairs, and array size with #.
• rules/variables.md. Naming for constants, locals over globals, and when an enum reads better than a boolean.
• rules/conditionals.md. Default values with or, boolean expressions and readability.
• rules/errors.md. Assertions, pre-conditions, errors as values and failing loudly instead of swallowing problems.
• rules/reference-links.md. Official Lua and FiveM documentation, including docs.fivem.net.

Common mistakes with Lua for FiveM

• Accidental globals. A missing local turns a variable into a global shared by every file in the resource. Symptom: values leak between scripts, a counter in one file changes in another, and global lookups are slower than locals. Fix: declare everything with local and treat a bare assignment as a bug.
• Indexing from 0. players[0] is nil and a for i = 0, #players loop starts on an empty slot. Symptom: the first entry is skipped, or the code errors on iteration zero. Fix: start at 1 and iterate with ipairs.
• Using # on the wrong table. #t is only defined for a sequence without holes. It ignores string keys, and with holes the result is unpredictable. Fix: keep a separate counter or iterate with pairs when the keys are not 1..n.
• Confusing false with nil. if x then fails for both nil and false. If false is a valid value, a default like x = x or true silently overrides it. Fix: write if x ~= nil then when false matters, and be careful with a and b or c when b can be false.
• Treating Lua like JavaScript. There is no != (use ~=), no continue (use goto continue or restructure), no ternary. Building big strings with .. inside loops creates a new string on every step. Fix: use table.concat for large output and write conditionals the Lua way.

Why AI assistants get Lua for FiveM wrong

A generic assistant writes Lua with the muscle memory of JavaScript and Python. It drops local, starts loops at 0, uses !=, invents a continue, and reaches for a and b or c as a ternary without noticing the false case. It also calls table.insert inside hot server loops because that is what every tutorial does. The code often runs and fails later, quietly, under load.

The Lua basics skill gives the assistant the five rule files and tells it to read the one that matches the task. Functions get guard clauses and small bodies, tables get 1-based loops with ipairs, variables are local by default, errors surface through assertions and pre-conditions instead of being ignored. The result reads like Lua written by someone who works on FiveM every day, which makes it far easier for you to review.

Install the Lua basics skill in 30 seconds

1. Click "Download SKILL.md" at the top of this page.
2. Unzip it into the skills or rules folder of your AI tool. The install section below shows the exact path for Claude Code, Cursor and VS Code.
3. Ask the assistant for something concrete, like "write a function that returns the players within 10 meters of a coordinate", and check that every variable is local, the loop uses ipairs and the function returns early on bad input.