diff --git a/presets/nes/aputest.c b/presets/nes/aputest.c
index 9e5527f8..c24edff9 100644
--- a/presets/nes/aputest.c
+++ b/presets/nes/aputest.c
@@ -1,4 +1,10 @@
 
+/*
+Generates random sounds in the APU, printing the parameters
+to the screen. Also shows an asterisk while each channel is
+playing, i.e. while its length counter is active.
+*/
+
 #include <stdlib.h>
 #include <stdio.h>
 #include <string.h>
diff --git a/presets/nes/attributes.c b/presets/nes/attributes.c
index c185a303..360e5799 100644
--- a/presets/nes/attributes.c
+++ b/presets/nes/attributes.c
@@ -1,4 +1,9 @@
 
+/*
+Setting the attribute table, which controls palette selection
+for the nametable. We copy it from an array in ROM to video RAM.
+*/
+
 #include "neslib.h"
 #include <string.h>
 #include <stdlib.h>
diff --git a/presets/nes/bankswitch.c b/presets/nes/bankswitch.c
index 69f88821..19155b31 100644
--- a/presets/nes/bankswitch.c
+++ b/presets/nes/bankswitch.c
@@ -1,4 +1,13 @@
 
+/*
+Bank-switching using the MMC3 mapper.
+We use a special linker config that sets up
+64 KB of PRG ROM and 64 KB of CHR ROM.
+Macros are used to set MMC3 registers and switch banks.
+CC65 #pragma directives are used to put things in various
+PRG ROM segments (CODE0-CODE6, CODE).
+*/
+
 // bank-switching configuration
 #define NES_MAPPER 4		// Mapper 4 (MMC3)
 #define NES_PRG_BANKS 4		// # of 16KB PRG banks
diff --git a/presets/nes/climber.c b/presets/nes/climber.c
index c8461bcc..20075cd7 100644
--- a/presets/nes/climber.c
+++ b/presets/nes/climber.c
@@ -1,4 +1,14 @@
 
+/*
+A platform game with a randomly generated stage.
+Uses the Famitone2 library for sound and music.
+It scrolls vertically (horizontal mirroring) and nametable
+updates are performed offscreen one row at a time with the
+draw_floor_line() function.
+The enemies use the same movement logic as the player, just
+with random inputs.
+*/
+
 #include <stdlib.h>
 #include <string.h>
 
diff --git a/presets/nes/fami.c b/presets/nes/fami.c
index 96de1caf..cdf9b7f5 100644
--- a/presets/nes/fami.c
+++ b/presets/nes/fami.c
@@ -1,4 +1,9 @@
 
+/*
+Demonstrates the Famitone2 library for sound and music.
+Press controller buttons to hear sound effects.
+*/
+
 #include "neslib.h"
 
 // link the pattern table into CHR ROM
diff --git a/presets/nes/flicker.c b/presets/nes/flicker.c
index 92818f98..0d68376b 100644
--- a/presets/nes/flicker.c
+++ b/presets/nes/flicker.c
@@ -1,4 +1,11 @@
 
+/*
+If you have more objects than will fit into the 64 hardware
+sprites, you can omit some of the sprites each frame.
+We also use oam_meta_spr_pal() to change the color of each
+metasprite.
+*/
+
 #include <stdlib.h>
 #include <string.h>
 
diff --git a/presets/nes/hello.c b/presets/nes/hello.c
index e7054e8d..a8cc3b49 100644
--- a/presets/nes/hello.c
+++ b/presets/nes/hello.c
@@ -1,4 +1,11 @@
 
+/*
+A simple "hello world" example.
+Set the screen background color and palette colors.
+Then write a message to the nametable.
+Finally, turn on the PPU to display video.
+*/
+
 #include "neslib.h"
 
 // link the pattern table into CHR ROM
diff --git a/presets/nes/horizmask.c b/presets/nes/horizmask.c
index be16c708..eb58337b 100644
--- a/presets/nes/horizmask.c
+++ b/presets/nes/horizmask.c
@@ -1,4 +1,15 @@
 
+/*
+We demonstrate horizontal scrolling of two nametables.
+Vertical mirroring is set, so nametables A and B are
+to the left and right of each other.
+
+New playfield data is randomly generated and updated
+offscreen using the vrambuf module.
+Every 32 pixels, we also update the attribute table.
+We also use the split() function to create a status bar.
+*/
+
 #include "neslib.h"
 #include <string.h>
 
@@ -29,11 +40,13 @@ byte bldg_attr;		// attribute table value
 
 #define PLAYROWS 24
 
+// convert from nametable address to attribute table address
 word nt2attraddr(word a) {
   return (a & 0x2c00) | 0x3c0 |
     ((a >> 4) & 0x38) | ((a >> 2) & 0x07);
 }
 
+// generate new random building data
 void new_building() {
   bldg_height = (rand8() & 7) + 2;
   bldg_width = (rand8() & 3) * 4 + 4;
@@ -41,6 +54,8 @@ void new_building() {
   bldg_attr = rand8();
 }
 
+// update the nametable offscreen
+// called every 8 horizontal pixels
 void update_nametable() {
   register word addr;
   // a buffer drawn to the nametable vertically
diff --git a/presets/nes/irq.c b/presets/nes/irq.c
index 5b1534df..2e327183 100644
--- a/presets/nes/irq.c
+++ b/presets/nes/irq.c
@@ -1,4 +1,12 @@
 
+/*
+Multiple screen splits with the MMC3 mapper using IRQs.
+The main loop updates the scroll counters continuously.
+When a IRQ fires, we change the X scroll register, setting
+it immediately via the PPU struct.
+The NMI and IRQ use the same callback function.
+*/
+
 // bank-switching configuration
 #define NES_MAPPER 4		// Mapper 4 (MMC3)
 #define NES_PRG_BANKS 4		// # of 16KB PRG banks
diff --git a/presets/nes/metacursor.c b/presets/nes/metacursor.c
index 8fc80a21..5890fa7e 100644
--- a/presets/nes/metacursor.c
+++ b/presets/nes/metacursor.c
@@ -1,4 +1,10 @@
 
+/*
+Read from controllers with pad_poll().
+We also demonstrate sprite animation by cycling among
+several different metasprites, which are defined using macros.
+*/
+
 #include <stdlib.h>
 #include <string.h>
 
diff --git a/presets/nes/metasprites.c b/presets/nes/metasprites.c
index 5cf55e49..5bd3f8d6 100644
--- a/presets/nes/metasprites.c
+++ b/presets/nes/metasprites.c
@@ -1,4 +1,10 @@
 
+/*
+Metasprites combine several hardware sprites to make a larger
+sprite. Our demo uses 4 hardware sprites in a 2x2 pattern,
+forming 16x16 pixel sprites.
+*/
+
 #include <stdlib.h>
 #include <string.h>
 
diff --git a/presets/nes/monobitmap.c b/presets/nes/monobitmap.c
index 4f54ac74..a25c7d9a 100644
--- a/presets/nes/monobitmap.c
+++ b/presets/nes/monobitmap.c
@@ -1,4 +1,12 @@
 
+/*
+Creates a monochrome frame buffer in video RAM.
+We map the pattern tables to CHR RAM, using the UxROM (2) mapper.
+By cleverly setting up palettes, and using a split-screen
+CHR bank switch, we split the screen into four different regions
+that display their own pixels.
+*/
+
 #include "neslib.h"
 #include "nes.h"
 #include <stdlib.h>
diff --git a/presets/nes/music.c b/presets/nes/music.c
index 5b758ad5..c1f817e7 100644
--- a/presets/nes/music.c
+++ b/presets/nes/music.c
@@ -1,4 +1,8 @@
 
+/*
+A simple music player.
+*/
+
 #include <string.h>
 #include <nes.h>
 
diff --git a/presets/nes/rletitle.c b/presets/nes/rletitle.c
index e10787aa..98c0c334 100644
--- a/presets/nes/rletitle.c
+++ b/presets/nes/rletitle.c
@@ -1,6 +1,8 @@
 
-// this example code unpacks a RLE'd nametable into the VRAM
-// you can create the source data using NES Screen Tool
+/*
+Unpacks a RLE-compressed nametable+attribute table into VRAM.
+Also uses the pal_bright() function to fade in the palette.
+*/
 
 #include "neslib.h"
 
diff --git a/presets/nes/scroll.c b/presets/nes/scroll.c
index 06e1b824..cdf336d7 100644
--- a/presets/nes/scroll.c
+++ b/presets/nes/scroll.c
@@ -1,4 +1,12 @@
 
+/*
+Scrolling demo.
+We've selected horizontal mirroring as the default, so
+nametables A and C are stacked on top of each other.
+The vertical scroll area is 480 pixels high; note how
+the nametables wrap around.
+*/
+
 #include "neslib.h"
 #include <string.h>
 
diff --git a/presets/nes/shoot2.c b/presets/nes/shoot2.c
index d106bdc1..fc55472c 100644
--- a/presets/nes/shoot2.c
+++ b/presets/nes/shoot2.c
@@ -1,4 +1,11 @@
 
+/*
+A shoot-em-up game.
+Uses CHR RAM to draw attacker tiles at 8 different pixels,
+then animates them in the nametable.
+Sprites are used for the player, missiles, attackers, and stars.
+*/
+
 #include <stdlib.h>
 #include <string.h>
 #include <nes.h>
diff --git a/presets/nes/siegegame.c b/presets/nes/siegegame.c
index a4690371..185d7308 100644
--- a/presets/nes/siegegame.c
+++ b/presets/nes/siegegame.c
@@ -1,4 +1,10 @@
 
+/*
+A character-based surround-the-opponent game.
+Reads from nametable RAM to determine collisions, and also
+to help the AI avoid walls.
+*/
+
 #include <stdlib.h>
 #include <string.h>
 #include <nes.h>
diff --git a/presets/nes/sprites.c b/presets/nes/sprites.c
index 322309e4..8d0e42ac 100644
--- a/presets/nes/sprites.c
+++ b/presets/nes/sprites.c
@@ -1,4 +1,9 @@
 
+/*
+Sprite demo.
+Animate all 64 hardware sprites.
+*/
+
 #include <stdlib.h>
 #include <string.h>
 
diff --git a/presets/nes/statusbar.c b/presets/nes/statusbar.c
index c827f83d..39c5c6a0 100644
--- a/presets/nes/statusbar.c
+++ b/presets/nes/statusbar.c
@@ -1,4 +1,12 @@
 
+/*
+Demo of split screen effect.
+We position sprite 0 at the desired scanline, and when it
+collides with the background, a flag in the PPU is set.
+The split() function waits for this flag, then changes the
+X scroll register in the PPU.
+*/
+
 #include "neslib.h"
 #include <string.h>
 
diff --git a/presets/nes/tint.c b/presets/nes/tint.c
index 9811e1d1..248bab99 100644
--- a/presets/nes/tint.c
+++ b/presets/nes/tint.c
@@ -1,4 +1,9 @@
 
+/*
+Demonstrates the PPU's tint and monochrome bits.
+Use the controller to see different combinations.
+*/
+
 #include <stdlib.h>
 #include <string.h>
 
diff --git a/presets/nes/vrambuffer.c b/presets/nes/vrambuffer.c
index e60a8ae6..16e61bce 100644
--- a/presets/nes/vrambuffer.c
+++ b/presets/nes/vrambuffer.c
@@ -1,4 +1,11 @@
 
+/*
+On the NES, you can't write to video RAM while the PPU
+is active, so you have to do it during the vertical blank.
+We have a module (vrambuf) which fills up a buffer with video
+data, then NESLib writes it to VRAM during the NMI interrupt.
+*/
+
 #include "neslib.h"
 #include <string.h>
 #include <stdio.h>
diff --git a/src/platform/nes.ts b/src/platform/nes.ts
index 6147f9c4..8d5d4db9 100644
--- a/src/platform/nes.ts
+++ b/src/platform/nes.ts
@@ -24,10 +24,10 @@ const JSNES_PRESETS = [
   {id:'monobitmap.c', name:'Monochrome Bitmap'},
   {id:'aputest.c', name:'Sound Tester'},
   {id:'music.c', name:'Music Player'},
+  {id:'fami.c', name:'Famitone Demo'},
   {id:'siegegame.c', name:'Siege Game'},
   {id:'shoot2.c', name:'Solarian Game'},
   {id:'climber.c', name:'Platform Game'},
-  {id:'fami.c', name:'Famitone Demo'},
   {id:'bankswitch.c', name:'Bank Switching'},
   {id:'irq.c', name:'IRQ Scanline Counter'},
   {id:'ex0.dasm', name:'Initialization (ASM)'},