Find out how to invite up to 500 friends (the maximum number possible with this method) to an event you create, from the Facebook website on the Google Chrome browser. Note that since February 2017, you can only do this from a desktop computer.
Steps
Part 1 of 2: install the Invite All Friends on Facebook extension

Step 1. Open the Invite All Friends on Facebook extension
You need to install it in Google Chrome and be signed in to your Chrome account to do this.
- If you see a silhouette icon at the top right of your browser window, and not your initials or Google+ profile, click that silhouette, and then click Log in.

Step 2. Click Add to Chrome
It's at the top right of the window. The extension will be installed in your Chrome browser.
Part 2 of 2: Invite Facebook Friends

Step 1. Go to the Facebook website

Step 2. Click on the Facebook logo
It's to the left of the search bar at the top of the window.

Step 3. Choose Events
It's on the left side of the window, under Explorer.

Step 4. Click + Create event
It's to the right of the window, towards the middle of the page.

Step 5. Select Create Private Event
This is the first option in the drop-down menu.
- Only guests can view private events.
- Public events are open to everyone on Facebook and do not require an invitation.

Step 6. Enter information about your event
Add the time, location and a title for your event.
You can also allow your friends to invite friends by checking the corresponding box at the bottom of this page

Step 7. Choose Create Private Event
It's at the bottom right of the dialog box.

Step 8. Click Invite
This is the drop-down menu on the right of the window.

Step 9. Choose Invite Facebook Friends

Step 10. Click All Friends
It's on the left of the dialog box.
There is no Select All feature for your All My Friends list

Step 11. Select some friends
Click the buttons next to the names of three or four friends, then deselect them.

Step 12. Click ✔️
It's the extension's logo and it appears to the right of the search bar at the top of the Chrome window.
- The extension will select all friends (up to 500) from your list.
- Facebook currently limits the number of invitations per event to 500 to avoid spam.

Step 13. Click Send Invitations
It's at the top right of the dialog box. The invitations will be sent to your friends.
Advice
You can simply duplicate the event you just created and edit its information, to avoid selecting all your friends individually
Warnings
- This method only works on the Facebook website opened in the Chrome browser.
- Avoid using codes or extensions that claim to be able to select all of your friends. All codes have been changed by Facebook and no longer work. Extensions are often accompanied by malware.