The client-side versus server-side distinction is the single most important concept in FiveM development. Understanding it explains why scripts are structured the way they are, why some things are exploitable, and why "server-side validation" matters so much. Here it is, explained simply.
The two sides
Every FiveM server has two sides:
The client is each player's own game, running on their PC. It handles what they see and do — graphics, input, animations, local UI. Crucially, the client can be modified by the player (cheaters do this).
The server is the single authoritative host that everyone connects to. It holds the real truth about the game world — who has what money, which jobs players hold, what's in the database. The server is trusted; clients are not.
A simple analogy
Imagine a shop. The client is a customer saying "I'd like to buy this, and here's what I claim I can afford." The server is the cashier who actually checks your money, takes payment, and hands over the item. If the cashier just believed whatever customers *claimed* they had, people would walk out with everything for free.
That's exactly the relationship. The client makes requests; the server verifies and decides.
Why this matters: security
Here's the critical consequence: because the client can be hacked, you can never trust it for anything important.
If a script lets the client decide how much money a player gets, a cheater edits their client and gives themselves millions. If the client decides whether a player owns a job, a cheater grants themselves police or admin. This is how exploits happen — scripts that trust the client for things only the server should decide.
The fix is server-side validation: the server checks every important action. "You want to switch to the police job? Let me verify on the server that you actually own it." "You want to sell this item? Let me confirm on the server you actually have it." This is why we stress server-side validation when discussing multijob systems and buying quality scripts — it's the line between secure and exploitable.
How scripts use both sides
A typical secure interaction:
- Client: player clicks "rob the store" → sends a request to the server
- Server: verifies the player can (are they in the right place? cooldown ok?) → grants the reward → updates the database
- Server: tells the relevant clients what happened
- Clients: show the result
The client handles presentation; the server handles truth and rewards. They communicate through events.
Why some things ARE client-side
Not everything belongs on the server. Purely visual or local things — animations, UI, local effects — happen client-side because they don't affect the shared truth and putting them on the server would be wasteful. The rule of thumb: presentation on the client, authority on the server.
What this means for you as a server owner
You don't have to code this, but understanding it helps you:
- Recognize why exploits happen — usually a script trusting the client
- Value server-side validation when choosing scripts
- Avoid sketchy scripts that might be insecure
- Understand the guidance in dev docs and guides
A script that does its security properly server-side is worth far more than one that looks the same but trusts the client.
Security built in
At Viper Development, our scripts validate important actions server-side — so players can't exploit them to grant themselves jobs, money, or items they shouldn't have. That security is invisible when it works, and critical when it matters. Browse our scripts →.