Server Properties

First, let's take a look to the settings you get as you launch the server at its first time.

#Minecraft server properties
#Wed May 03 16:48:18 CEST 2017
max-tick-time=60000
generator-settings=
force-gamemode=false
allow-nether=true
gamemode=0
enable-query=false
player-idle-timeout=0
difficulty=1
spawn-monsters=true
op-permission-level=4
announce-player-achievements=true
pvp=true
snooper-enabled=true
level-type=DEFAULT
hardcore=false
enable-command-block=false
max-players=20
network-compression-threshold=256
resource-pack-sha1=
max-world-size=29999984
server-port=25565
server-ip=
spawn-npcs=true
allow-flight=false
level-name=world
view-distance=10
resource-pack=
spawn-animals=true
white-list=false
generate-structures=true
online-mode=true
max-build-height=256
level-seed=
prevent-proxy-connections=false
enable-rcon=false
motd=A Minecraft Server

And now let's talk about what is each setting and value:

Key	Description
max-tick-time	The maximum number of milliseconds a single tick may take before the server watchdog stops the server with the message
generator-settings	The settings used to customize world generation. See Superflat and Customized for possible settings and examples.
force-gamemode	Force players to join in the default game mode. false - Players will join in the gamemode they left in. true - Players will always join in the default gamemode.
allow-nether	Allows players to travel to the Nether. false - Nether portals will not work. true - The server will allow portals to send players to the Nether.
gamemode	Defines the mode of gameplay. 0 - Survival 1 - Creative 2 - Adventure 3 - Spectator
enable-query	Enables GameSpy4 protocol server listener. Used to get information about server.
player-idle-timeout	If non-zero, players are kicked from the server if they are idle for more than that many minutes. Note: Idle time is reset when the server receives one of the following packets: Click Window Enchant Item Update Sign Player Digging Player Block Placement Held Item Change Animation (swing arm) Entity Action Client Status Chat Message Use Entity
difficulty	Defines the difficulty (such as damage dealt by mobs and the way hunger and poison affects players) of the server. 0 - Peaceful 1 - Easy 2 - Normal 3 - Hard
spawn-monsters	Determines if monsters will be spawned. true - Enabled. Monsters will appear at night and in the dark. false - Disabled. No monsters. This setting has no effect if difficulty = 0 (peaceful). If difficulty is not = 0, a monster can still spawn from a Monster Spawner. Tip: if you have major lag, turn this off/set to false.
op-permission-level	Sets the default permission level for ops when using /op. All levels inherit abilities and commands from levels before them. 1 - Ops can bypass spawn protection. 2 - Ops can use all singleplayer cheats commands (except /publish, as it is not on servers; along with /debug) and use command blocks. Command blocks and Realms operators/owners have this level. 3 - Ops can use most multiplayer-exclusive commands (all except level 4 commands). 4 - Ops can use all commands including /stop, /save-all, /save-on, and /save-off
announce-player-achievements	Allows server to announce when a player gets an achievement. (True /False)
pvp	Enable PvP on the server. Players shooting themselves with arrows will only receive damage if PvP is enabled. true - Players will be able to kill each other. false - Players cannot kill other players (also known as Player versus Environment (PvE)).
snooper-enabled	Sets whether the server sends snoop data regularly to http://snoop.minecraft.net. false - disable snooping. true - enable snooping.
level-type	Determines the type of map that is generated. DEFAULT - Standard world with hills, valleys, water, etc. FLAT - A flat world with no features, meant for building. LARGEBIOMES - Same as default but all biomes are larger. AMPLIFIED - Same as default but world-generation height limit is increased. CUSTOMIZED - Same as default unless generator-settings is set to a preset.
hardcore	If set to true, players will be set to spectator mode if they die.
enable-command-block	Enables command blocks
max-players	The maximum number of players that can play on the server at the same time. Note that if more players are on the server it will use more resources. Note also, op player connections are not supposed to count against the max players, but ops currently cannot join a full server. Extremely large values for this field result in the client-side user list being broken.
network-compression-threshold	By default it allows packets that are n-1 bytes big to go normally, but a packet that n bytes or more will be compressed down. So, lower number means more compression but compressing small amounts of bytes might actually end up with a larger result than what went in. -1 - disable compression entirely 0 - compress everything
resource-pack-sha1	Optional SHA-1 digest of the resource pack, in lowercase hexadecimal. It's recommended to specify this. This is not yet used to verify the integrity of the resource pack, but improves the effectiveness and reliability of caching.
max-world-size	This sets the maximum possible size in blocks, expressed as a radius, that the world border can obtain. Setting the world border bigger causes the commands to complete successfully but the actual border will not move past this block limit. Setting the max-world-size higher than the default doesn't appear to do anything. Examples: Setting max-world-size to 1000 will allow you to have a 2000x2000 world border. Setting max-world-size to 4000 will give you an 8000 x 8000 world border.
server-port	Changes the port the server is hosting (listening) on. This port must be forwarded if the server is hosted in a network using NAT (If you have a home router/firewall).
server-ip	Set this if you want the server to bind to a particular IP. It is strongly recommended that you leave server-ip blank! Set to blank, or the IP you want your server to run (listen) on.
spawn-npcs	Determines whether villagers will be spawned. true - Enabled. Villagers will spawn. false - Disabled. No villagers.
allow-flight	Allows users to use flight on your server while in Survival mode, if they have a mod that provides flight installed. With allow-flight enabled, griefers will possibly be more common, because it will make their work easier. In Creative mode this has no effect. false - Flight is not allowed (players in air for at least 5 seconds will be kicked). true - Flight is allowed, and used if the player has a fly mod installed
level-name	The "level-name" value will be used as the world name and its folder name. You may also copy your saved game folder here, and change the name to the same as that folder's to load it instead. Characters such as ' (apostrophe) may need to be escaped by adding a backslash before them.
view-distance	Sets the amount of world data the server sends the client, measured in chunks in each direction of the player (radius, not diameter). It determines the server-side viewing distance. (see Render distance) 10 is the default/recommended. If you have major lag, reduce this value.
resource-pack	Optional URI to a resource pack. The player may choose to use it.
spawn-animals	Determines if animals will be able to spawn. true - Animals spawn as normal. false - Animals will immediately vanish. Tip: if you have major lag, turn this off/set to false.
white-list	Enables a whitelist on the server. With a whitelist enabled, users not on the whitelist will be unable to connect. Intended for private servers, such as those for real-life friends or strangers carefully selected via an application process, for example. false - No white list is used. true - The file whitelist.json is used to generate the white list. Note: Ops are automatically white listed, and there is no need to add them to the whitelist.
generate-structures	Defines whether structures (such as villages) will be generated. false - Structures will not be generated in new chunks. true - Structures will be generated in new chunks. Note: Dungeons will still generate if this is set to false.
online-mode	Server checks connecting players against Minecraft's account database. Only set this to false if your server is not connected to the Internet. Hackers with fake accounts can connect if this is set to false! If minecraft.net is down or inaccessible, no players will be able to connect if this is set to true. Setting this variable to off purposely is called "cracking" a server, and servers that are presently with online mode off are called "cracked" servers, allowing players with unlicensed copies of Minecraft to join. true - Enabled. The server will assume it has an Internet connection and check every connecting player. false - Disabled. The server will not attempt to check connecting players.
max-build-height	The maximum height in which building is allowed. Terrain may still naturally generate above a low height limit.
level-seed	Add a seed for your world, as in Singleplayer.
prevent-proxy-connections	If the ISP/AS sent from the server is different from the one from Mojang's authentication server, the player is kicked true - Enabled. Server prevents users from using vpns or proxies. false - Disabled. The server doesn't prevent users from using vpns or proxies.
enable-rcon	Enables remote access to the server console.
motd	This is the message that is displayed in the server list of the client, below the name. The MOTD does support color and formatting codes. The MOTD supports special characters, such as "♥". However, such characters must be converted to escaped Unicode form. An online converter can be found here If the MOTD is over 59 characters, the server list will likely report a communication error.