Offside Checker: The Free Online Tool for Football Fans
With our offside checker tool, you'll be able to analyze and judge for yourself if a player is on a offside position.
We created this because every football fan has been there. The ball hits the net. Then the flag goes up, or the VAR screen lights up, and suddenly everyone is arguing about millimetres.
Was he offside? Was his armpit past the defender's knee? Who even decides what counts as a body part?
We built this tool so you don't have to take anyone's word for it.
What Is an Offside Checker?
An offside checker is a tool that lets you draw the official offside lines on any football screenshot yourself, accounting for the camera angle and perspective distortion that makes these calls so hard to judge with the naked eye.
Our Football Offside Checker is free, runs entirely in your browser, and requires no login or account.
You upload a screenshot, calibrate the perspective of the pitch, place two lines, one on the last defender, one on the attacker, and get an instant verdict.
It is the same logic VAR uses. Without the broadcast monopoly.
Why Offside Lines Are Harder Than They Look
The problem with judging offside from a television broadcast is perspective.
Cameras are positioned at an angle to the pitch, not directly overhead. This means a straight vertical line drawn on the screen will be wrong, it won't follow the actual plane of the pitch. A player who looks offside from one camera angle can be clearly onside from another.
Professional VAR systems correct for this using a process called perspective calibration. They identify known reference points on the pitch (the edges of the penalty box, the six-yard box, the halfway line) and use them to calculate the true angle of any line drawn on the image.
Our offside checker does exactly this. Before you place the offside lines, you calibrate by clicking the four corners of any rectangular marking you can see on the pitch. The tool then draws all subsequent lines following the correct perspective along the true plane of the football field.
The result is a line that matches what VAR should be drawing.
How to Use the Football Offside Checker
Using the tool takes less than a minute. Here is the full process:
Step 1 — Get your screenshot
Take a screenshot from a broadcast, a clip on X, or a YouTube video. Pause at the exact moment the ball is played, that is the moment the offside position is judged, not when the player receives it. Use Ctrl+V to paste it directly into the tool, or click Upload.
Step 2 — Calibrate the perspective
Click the four corners of a rectangular pitch marking you can see in the image. Go top-left to top-right, then bottom-right to bottom-left. You can always readjust these points if needed. The penalty box and six-yard box work best.
The tool draws a yellow calibration box and a grid, if the grid lines align with the pitch markings, your calibration is accurate.
Step 3 — Place the defender and attacker lines
Click on the last outfield defender, specifically on the part of their body that is furthest forward. Under the current rules, any body part that can legally score a goal counts, so if you have to mark the shoulder, head or knee, a white vertical dashed line will help you get that reference point.
A red line appears, following the perspective you calibrated.
Now you can click on the attacker's furthest forward body part at the moment the ball is played. A blue line appears.
Step 4 — Read the verdict
The tool compares the two lines and displays the verdict instantly. OFFSIDE in red or ONSIDE in green.
You can drag either line to fine-tune the position. You can also toggle the attack direction if the team is playing left to right or right to left.
When you are done, hit Download or Copy Image to save the annotated image on your files or clipboard and share it.
Who This Tool Is For
Fans who want to check a controversial call from the weekend's matches before arguing about it online.
Content creators who cover football and want to include proper visual analysis in their videos or posts.
Journalists who need a quick sanity check on a VAR decision without access to professional broadcast tools.
Anyone who is tired of being told to trust the process.
Try It Now
The tool is free. No account. No subscription. No data collected.
Open the Football Offside Checker, paste your screenshot, and find out for yourself.
If you find a call that looks wrong and the lines prove it, submit your story. That is exactly what this site is for.