Examples and ideas.
The colours are a bit random. Sure, it doesn't make for the most coherent user interface. Oh well. You'll cope.
No save. Right click does things. You can open multiple browser tabs to keep track of things. Or screen shots. You will lose work. Sorry.
No way to print or save to a PDF. Feedback and ideas needed before I code this.Help
Squares, walls, clutter: Click and a room will appear. Keep clicking and more rooms. Click on a room and it may delete (or turn into a door see below.) Clutter and hatching is random
Doors: draw a room 1x3 squares. Click on the middle square - boom - a door appears.
Boulders: These are a bit random. Scatter - scatters a few around. Don't like what you see? Click on it to delete it and try again. Life is random. So are boulders.
Text: Text with no background. Useful to label things. You can experiment. e.g. use a # for treasure chest, or > for a trap, or an O for a mystical pool. It's ascii art. You'll figure out some neat uses for it. I trust you.
Banners: I like b1 for lower case text. Its upper case letters suck. I like b2 for upper case text. Feel free to break those rules. I don't mind. Try entering a few spaces followed by a ! then use a pen to write your own label.
Tip 1: You have a pen. Print the dungeon and use your pen on it. Highlighers. Post-it notes.
Tip 2: Line of sight. Use scisors to cut up the dungeon. Reveal it to your players. Use the labels to help organise the 'jigsaw'. Tape it together. Nothing is more enticing to a player than a locked door with a big blank space behind it. You can design a dungeon so that the players can choose to go East or West, but as a DM you reveal the room with encounter 1 and clue 1 in whichever direction they choose.
Tip 3: Narrow coridoors are choke points.
Tip 4: Prison cells. Treasure rooms. Traps. Sleeping quaters. Rec rooms. Pits. Stables. Temple. Cave in. Rotten planks. River. Flavour. Walk-ways. Ladders. Acid pools. NPCs. Clue. Shop. Fireplace. Upstairs? Downstairs? How deep is this place?
Tip 5: Tension and fear. "You hear a roar echoing through the dungeon." ... "You find a human foot. Mostly eaten." ... "Three weeks later you have finally dug through the cave in" ... "Something senses you"
Tip 6: The world is not static. Who is following the group? Who is running from them? What is hunting them? When they rest - what runs into them? Can the players lay in ambush? What do they see at the end of the coridoor? Hear behind a door?
Tip 7: Players should label the map. Encourage this. It is their game. Let them own it.
Tip 8: It's not a dungeon, it's a market, a crashed spaceship, a fallen tower, a sea cave, a mansion, a fort, mud huts, termite mound, guts of a giant worm, bee hive, rotten tree.
Tip 9: Snipping tool. Win + SHIFT + s. paint.net