Press Left Mouse Button to start creating an area where NPCs will be spawned.
Press the button to confirm the area. Now you can change the angle NPCs will be spawned at.
Left click again to confirm the angle.

Now, when your area is completely ready, you can press Right Mouse Button to spawn NPCs.
You can place infinite amount of areas before you do this.
For example, you can made one area of hostile NPCs and another one of friendly NPCs, and then spawn them at once so they appear evenly across the map.

For your convenience, spread and random parameters were bound to the Mouse Wheel.
When creating area, use Up and Down Mouse Wheel to change the spread multiplier. It will increase or decrease the size of the grid.
Or hold the Shift Key to change randomness of NPC spawn instead.


Garry's Mod runs on 17 years old engine, obviously you don't want to spawn millions of NPCs.
Just try spawning 50 citizen NPCs the normal way and see how low your FPS becomes.
This tool is not for fun, it just makes the gmod experience better.


Some of the workshop NPC addons are poorly coded. There's no way to make the tool work with them.
NPCs should be actually NPCs or NextBots (i.e. pass npc:IsNPC() or npc:IsNextBot()) check).
SNPCs, VJBase and similar NPCs will work just fine.


Spawn flags adjust NPC behaviour, they are hardcoded in engine and supposed to be used by developers only. Use them only if you know how they work.
Note that some of these flags are necessary for some NPCs and will be forced anyway.
Some flags will not work for some NPCs.


No, it will ignore places where NPC spawn is impossible.
It's safe to use the tool everywhere, there's no need to avoid twisted corridors.


No, there's no data or entities to save or to be duped.
Spawn areas exist only in memory, therefore you can't use this tool with default gmod duplicator, AdvDupe, PermaProp or saves.


All NPCs in games powered by Source Engine can be assigned to squads.
Squads allow you to group NPCs for their further cooperation.
Members of squad cover each other, move together, share information, and take turns at attacking their enemies.

In Garry's Mod most NPCs are being assigned to specific squads when spawning by default.
For example most of the combine NPCs will be assigned to squad called "overwatch".
Whereas Nova Prospekt guards and shotgunners will have their own squad - "novaprospekt".

If you don't specify custom squad, all NPCs you spawn with the tool will be assigned to their default squads.
For instance, if you place two groups of the NPCs in different map areas, and warn one of these group, the other one will know about your presence.
You should consider that when creating long battles or events.

For more details visit Official Valve Wiki.