Chat

Minecraft supports two-way chat communication via the Protocol#Chat_Message packet

Current system (JSON Chat)

Comments (//) are not valid json and shouldn't be sent, they are only here to explain the format

 {
     // Plain text
     "text": "Hello world",
     //or
     // Translatable string
     "translate": "multiplayer.player.joined",
     "with": [
         //This can be replaced another json object allowing the parts
         //to be styled/translated seperately
         "thinkofdeath"
     ],
     //or
     // Displays the player's value for a scoreboard objective
     "score": {
         "name": "<playername>", // * for current player
         "objective": "<objectivename>"
     },
     //or
     // A standard minecraft selector, eg: @p, @a, @e, @r
     "selector": "",
     //
     //Items in the extra section will be appended to the message.
     //They can strings or json objects. If included the array must 
     //not be empty
     "extra": [
         "Testing",
         {"translate":"demo.day.2"}
     ],
     //Controls whether the text is bold or not. Default false
     "bold":true,
     //Controls whether the text is italic or not. Default false
     "italic":false,
     //Controls whether the text is underlined or not. Default false
     "underlined": false, 
     //Controls whether the text is striked out or not. Default false
     "strikethrough": false,
     //Controls whether the text is randomised constantly or not. Default false
     "obfuscated": false,
     //Controls the color of the text
     //Supported 'colors':
     // * black
     // * dark_blue
     // * dark_green
     // * dark_aqua
     // * dark_red
     // * dark_purple
     // * gold
     // * gray
     // * dark_gray
     // * blue
     // * green
     // * aqua
     // * red
     // * light_purple
     // * yellow
     // * white
     // * obfuscated
     // * bold
     // * strikethrough
     // * underline
     // * italic
     // * reset
     "color":"red",
     //Executes the action once the text is clicked
     "clickEvent":{
         //The action to execute
         //Supported actions:
         // * open_url
         // * open_file
         // * run_command
         // * suggest_command
         "action":"run_command",
         //The value to run the action with
         //open_url: Url to open
         //open_file: File to open
         //run_command: Command to execute
         //suggest_command: Text to place in the player's text box
         "value": "/time set day"
     },
     //Displays the action upon hovering over the text
     "hoverEvent": {
         //The action to execute
         //Supported actions
         // * show_text
         // * show_achievement
         // * show_item
         "action":"show_text",
         //The value to the action with
         //show_text: Text to display can be a JSON object
         //show_achievement: Name of the achievemnt to display e.g: "achievement.openInventory"
         //show_item: JSON version of the item, must be quoted. e.g: "{id:35,Damage:5,Count:2,tag:{display:{Name:Testing}}}"
         "value": "Hello"
     },
     // Inserts the text into the chat on shift click (1.8+)
     "insertion": "Hello world"   
 }

Old system

Control Sequences

The client treats certain two-character sequences specially. The first character must be:

• § (U+00A7) for minecraft
• & for minecraft classic

The following character indicates a certain colour or formatting to apply to the proceeding text.

The Notchian client expects that an escape code in a chat message will be followed by at least one character, and will otherwise crash with a StringIndexOutOfBoundsException. The workaround for servers is to never end a message with a color control character.

Colors

These correspond very roughly to the colors available in ANSI terminals.

e.g.: This is white, but §4this is dark red

Hex digit to color mapping

Sample	Code	Common Name	Foreground Color			Background Color			Hexadecimal
			R	G	B	R	G	B
	0	Black	0	0	0	0	0	0	#000000
	1	Dark blue	0	0	170	0	0	42	#0000aa
	2	Dark green	0	170	0	0	42	0	#00aa00
	3	Dark cyan	0	170	170	0	42	42	#00aaaa
	4	Dark red	170	0	0	42	0	0	#aa0000
	5	Purple	170	0	170	42	0	42	#aa00aa
	6	Gold	255	170	0	42	42	0	#ffaa00
	7	Gray	170	170	170	42	42	42	#aaaaaa
	8	Dark gray	85	85	85	21	21	21	#555555
	9	Blue	85	85	255	21	21	63	#5555ff
	a	Bright green	85	255	85	21	63	21	#55ff55
	b	Cyan	85	255	255	21	63	63	#55ffff
	c	Red	255	85	85	63	21	21	#ff5555
	d	Pink	255	85	255	63	21	63	#ff55ff
	e	Yellow	255	255	85	63	63	21	#ffff55
	f	White	255	255	255	63	63	63	#ffffff

Styles

Like the color codes above, style escape codes are created by combining § (U+00A7) with one of the following characters. Style codes can be combined (except for "r") to enable multiple effects at once. Using any color codes will reset the current style back to plain (unknown if this is a bug or intended behavior). The "r" plain style code will also reset the current chat color back to white (may also be a bug). The "k" random style code is used for the "§kFUNKY LOL" message in /title/splashes.txt inside minecraft.jar.

Sample	Code	Style
	k	Random
	l	Bold
	m	Strikethrough
	n	Underlined
	o	Italic
	r	Plain White

Font

Minecraft has two fonts types: Default (default.png) and Unicode(glyph_XX.png). Default will fallback on unicode characters if they are not provided (default only has the first 256 glyphs). The minecraft client calculates the widths of the default font type on startup whilst the sizes of the unicode type are provided in glyph_sizes.bin. Each byte in glyph_sizes.bin contains the start and end position of each character, the top nibble (0xF0) is the start position and the bottom nibble (0x0F) is the end position (relative to the characters position in the font sheet).

Example: https://gist.github.com/TkTech/dff9bbe54c9a074612e1