Slither.io Protocol Version 11

Note: all values are unsigned.

Clientbound

Every packet that comes from the server starts with a 3 byte header, which indicates the message type. The game converts the Message Type byte to a unicode characters so I will only list the character representations.

Most packets start like this:

Byte	Meaning
0-1	Time since last message to client
2	Message Type
3-4	Snake ID

Message Types

Type Identifier	Meaning
6	Pre-init response
a	Initial setup
e	Snake rotation counterclockwise (?dir ang ?wang ?sp)
E	Snake rotation counterclockwise (dir wang ?sp)
3	Snake rotation counterclockwise (dir ang wang \| sp)
4	Snake rotation clockwise (dir ang? wang ?sp)
5	Snake rotation clockwise (dir ang wang)
h	Update snake last body part fullness (fam)
r	Remove snake part
g	Move snake
G	Move snake
n	Increase snake
N	Increase snake
l	Leaderboard
v	dead/disconnect packet
W	Add Sector
w	Remove Sector
m	Global highscore
p	Pong
u	Update minimap
s	Add/remove Snake
F	Add Food
b	Add Food
f	Add Food
c	Food eaten
j	Update Prey
y	Add/remove Prey
o	Verify code response
k	Kill (unused in the game-code)

Packet "6" (Pre-init response)

This is the first packet received. It is an encoded JavaScript-file that the client executes. It generates a string, that is further manipulated by the client and sent back to the server. This is done for verification / bot-protection (if the clients answer is wrong, the connection is closed). After that, the client continues with the SetUsernameAndSkin-Packet.

Byte	DataType	Description
3-?	encoded string	JavaScript-expressions

Here is some Java-code for how to get the correct answer to send to the server:

private static byte[] decodeSecret(int[] secret) {

    byte[] result = new byte[24];

    int globalValue = 0;
    for (int i = 0; i < 24; i++) {
        int value1 = secret[17 + i * 2];
        if (value1 <= 96) {
            value1 += 32;
        }
        value1 = (value1 - 98 - i * 34) % 26;
        if (value1 < 0) {
            value1 += 26;
        }

        int value2 = secret[18 + i * 2];
        if (value2 <= 96) {
            value2 += 32;
        }
        value2 = (value2 - 115 - i * 34) % 26;
        if (value2 < 0) {
            value2 += 26;
        }

        int interimResult = (value1 << 4) | value2;
        int offset = interimResult >= 97 ? 97 : 65;
        interimResult -= offset;
        if (i == 0) {
            globalValue = 2 + interimResult;
        }
        result[i] = (byte) ((interimResult + globalValue) % 26 + offset);
        globalValue += 3 + interimResult;
    }

    return result;
}

Notice that while this currently works, it is possible that the official servers will use more complex "riddles" soon that won't work any more.

Packet "a" (Initial setup)

Tells the Client some basic information. The original client has some hard-coded values for these constants, but they get overridden by this packet. After the message arrives, the game calls "startShowGame();"

Bytes	Data Type	Description	Hard-coded defaults	Typical response
3-5	int24	Game Radius	16384	21600
6-7	int16	mscps (maximum snake length in body parts units)	300	411
8-9	int16	sector_size	480	300
10-11	int16	sector_count_along_edge (unused in the game-code)	130	144
12	int8	spangdv (value / 10) (coef. to calculate angular speed change depending snake speed)	4.8	4.8
13-14	int16	nsp1 (value / 100) (Maybe nsp stands for "node speed"?)	4.25	5.39
15-16	int16	nsp2 (value / 100)	0.5	0.4
17-18	int16	nsp3 (value / 100)	12	14
19-20	int16	mamu (value / 1E3) (basic snake angular speed)	0.033	0.033
21-22	int16	manu2 (value / 1E3) (angle in rad per 8ms at which prey can turn)	0.028	0.028
23-24	int16	cst (value / 1E3) (snake tail speed ratio )	0.43	0.43
25	int8	protocol_version	2	11

sct is a snake body parts count (length) taking values between [2 .. mscps]. fpsls[mscps] contains snake volume (score) to snake length in body parts units. 1/fmlts[mscps] contains body part volume (score) to certain snake length.

Total snake score equals:

    Math.floor(15 * (fpsls[snake.sct] + snake.fam / fmlts[snake.sct] - 1) - 5) / 1

sct - snake length in body parts units. sc - snake body part size? dep. on snake length. scang - change ratio of snake angular speed by snake thickness.

    f.sc = Math.min(6, 1 + (f.sct - 2) / 106);
    f.scang = .13 + .87 * Math.pow((7 - f.sc) / 6, 2);

Relation between nsp1, nsp2 and sc of unknown meaning.

    f.ssp = nsp1 + nsp2 * f.sc;
    f.fsp = f.ssp + .1;
    f.wsep = 6 * f.sc;

sp - snake speed. spangdv - coef. to calculate angular speed change depending snake speed. spang - change ratio of snake angular speed by movement speed.

    f.spang = f.sp / spangdv;
    1 < f.spang && (f.spang = 1);

mamu - basic snake angular speed. vfr - frames count spent. spang - influence of snake speed. scang - influence of snake length.

    eang = mamu * vfr * e.scang * e.spang;

Packet "e" (Snake rotation counterclockwise (?dir ang ?wang ?sp))

Update snake rotation direction. There are 4 parameters (direction, angle, wanted angle, speed) which combination determines rotation packet type "e", "E", "3", "4", "5" and set of serialized fields. Exact set of fields evaluation based on packet type and packet length. Fields always follow same ordering (snakeId < ang? < wang? < sp?). Thus, having 5 packet types, and up to 3 possible length reduce, we've got up to 12 useful cases.

If packet length is 6 + 2, then rotation direction is counterclockwise:

Bytes	Data type	Description
3-4	int16	Snake id
5	int8	ang * pi2 / 256 (current snake angle in radians, clockwise from (1, 0))
6	int8	wang * pi2 / 256 (target rotation angle snake is heading to)
7	int8	sp / 18 (snake speed?)

If packet length is 5 + 2, then rotation defined by the angle:

Bytes	Data type	Description
3-4	int16	Snake id
5	int8	ang * pi2 / 256 (current snake angle in radians, clockwise from (1, 0))
6	int8	sp / 18 (snake speed?)

If packet length is 4 + 2, then rotation defined by the angle:

Bytes	Data type	Description
3-4	int16	Snake id
5	int8	ang * pi2 / 256 (current snake angle in radians, clockwise from (1, 0))

Most used packets are "e" and "4", then "5" and "3".

Packet "E" (Snake rotation counterclockwise (dir wang ?sp))

Update snake rotation direction. There are 4 parameters (direction, angle, wanted angle, speed) which combination determines rotation packet type "e", "E", "3", "4", "5" and set of serialized fields. Exact set of fields evaluation based on packet type and packet length. Fields always follow same ordering (snakeId < ang? < wang? < sp?). Thus, having 5 packet types, and up to 3 possible length reduce, we've got up to 12 useful cases.

If packet length is 5 + 2, then rotation is counterclockwise:

Bytes	Data type	Description
3-4	int16	Snake id
5	int8	wang * pi2 / 256 (target rotation angle snake is heading to)
6	int8	sp / 18 (snake speed?)

If packet length is 4 + 2, then rotation is counterclockwise:

Bytes	Data type	Description
3-4	int16	Snake id
5	int8	wang * pi2 / 256 (target rotation angle snake is heading to)

Packet "3" (Snake rotation counterclockwise (dir ang wang | sp))

Update snake rotation direction. There are 4 parameters (direction, angle, wanted angle, speed) which combination determines rotation packet type "e", "E", "3", "4", "5" and set of serialized fields. Exact set of fields evaluation based on packet type and packet length. Fields always follow same ordering (snakeId < ang? < wang? < sp?). Thus, having 5 packet types, and up to 3 possible length reduce, we've got up to 12 useful cases.

If packet length is 5 + 2, then rotation direction is counterclockwise:

Bytes	Data type	Description
3-4	int16	Snake id
5	int8	ang * pi2 / 256 (current snake angle in radians, clockwise from (1, 0))
6	int8	wang * pi2 / 256 (target rotation angle snake is heading to)

If packet length is 4 + 2, then packet contains speed only:

Bytes	Data type	Description
3-4	int16	Snake id
5	int8	sp / 18 (snake speed?)

Most used packets are "e" and "4", then "5" and "3".

Packet "4" (Snake rotation clockwise (dir ang? wang ?sp))

Update snake rotation direction. There are 4 parameters (direction, angle, wanted angle, speed) which combination determines rotation packet type "e", "E", "3", "4", "5" and set of serialized fields. Exact set of fields evaluation based on packet type and packet length. Fields always follow same ordering (snakeId < ang? < wang? < sp?). Thus, having 5 packet types, and up to 3 possible length reduce, we've got up to 12 useful cases.

If packet length is 6 + 2, then rotation direction is clockwise:

Bytes	Data type	Description
3-4	int16	Snake id
5	int8	ang * pi2 / 256 (current snake angle in radians, clockwise from (1, 0))
6	int8	wang * pi2 / 256 (target rotation angle snake is heading to)
7	int8	sp / 18 (snake speed?)

If packet length is 5 + 2, then rotation direction is clockwise:

Bytes	Data type	Description
3-4	int16	Snake id
5	int8	wang * pi2 / 256 (target rotation angle snake is heading to)
6	int8	sp / 18 (snake speed?)

If packet length is 4 + 2, then packet contains speed only:

Bytes	Data type	Description
3-4	int16	Snake id
5	int8	wang * pi2 / 256 (target rotation angle snake is heading to)

Most used packets are "e" and "4", then "5" and "3".

Packet "5" (Snake rotation clockwise (dir ang wang))

Update snake rotation direction. There are 4 parameters (direction, angle, wanted angle, speed) which combination determines rotation packet type "e", "E", "3", "4", "5" and set of serialized fields. Exact set of fields evaluation based on packet type and packet length. Fields always follow same ordering (snakeId < ang? < wang? < sp?). Thus, having 5 packet types, and up to 3 possible length reduce, we've got up to 12 useful cases.

If packet length is 5 + 2, then rotation direction is clockwise:

Bytes	Data type	Description
3-4	int16	Snake id
5	int8	ang * pi2 / 256 (current snake angle in radians, clockwise from (1, 0))
6	int8	wang * pi2 / 256 (target rotation angle snake is heading to)

If packet length is 4 + 2, then packet contains speed only:

Bytes	Data type	Description
3-4	int16	Snake id
5	int8	wang * pi2 / 256 (target rotation angle snake is heading to)

Most used packets are "e" and "4", then "5" and "3".

Packet "h" (Update snake last body part fullness (fam))

Update the fam-value (used for length-calculation) of a snake. fam is a float value (usually in [0 .. 1.0]) representing a body part ratio before changing snake length sct in body parts. Snake gets new body part when fam reaches 1, and looses 1, when fam reaches 0.

Bytes	Data type	Description
3-4	int16	Snake id
5-7	int24	value / 16777215 -> fam

Packet "r" (Remove snake part)

Removes the last part from this snake.

Variant 1: packet-size = 5

Bytes	Data type	Description
3-4	int16	Snake id

Variant 2: packet-size = 8

Bytes	Data type	Description
3-4	int16	Snake id
5-7	int24	snake.fam fullness (value / 16777215))

Packet "g" (Move snake)

Move snake into new position.

Bytes	Data type	Description
3-4	int16	Snake id
5-6	int16	x
7-8	int16	y

Packet "G" (Move snake)

Move snake into new position.

Bytes	Data type	Description
3-4	int16	Snake id
5	int8	value - 128 + head.x -> x
6	int8	value - 128 + head.y -> y

Packet "n" (Increase snake)

Move snake into new position and increase snake body length by 1 body-part. The fam-value is updated.

Bytes	Data type	Description
3-4	int16	Snake id
5-6	int16	x
7-8	int16	y
9-11	int24	value / 16777215 -> fam

Packet "N" (Increase snake)

Move snake into new position and increase snake body length by 1 body-part. The fam-value is updated.

Bytes	Data type	Description
3-4	int16	Snake id
5	int8	value - 128 + head.x -> x
6	int8	value - 128 + head.y -> y
7-9	int24	value / 16777215 -> fam

Packet "l" (Leaderboard)

Packet "l" is required for displaying the leaderboard.

Starting at byte 6 are the top ten players.

Bytes	Data type	Description
3	int8	local players rank in leaderboard (0 means not in leaderboard, otherwise this is equal to the "local players rank". Actually always redundant information)
4-5	int16	local players rank
6-7	int16	players on server count
?-?	int16	snake body parts count (sct)
?-?	int24	snake last body part fullness (fam / 16777215)
?-?	int8	font color (between 0 and 8)
?-?	int8	username length
?-?	string	username

Snake score / length:

    Math.floor(15 * (fpsls[snake.sct] + snake.fam / fmlts[snake.sct] - 1) - 5) / 1

Packet "v" (dead/disconnect packet)

Sent when player died.

Bytes	Data type	Description
3	int8	0-2; 0 is normal death, 1 is new highscore of the day, 2 is unknown (disconnect??)

Packet "W" (Add Sector)

Sent when a new Sector becomes active for the client.

Bytes	Data type	Description
3	int8	x-coordinate of the new sector
4	int8	y-coordinate of the new sector

Packet "w" (Remove Sector)

Sent when a Sector should be unloaded.

Bytes	Data type	Description
3	int8	x-coordinate of the sector
4	int8	y-coordinate of the sector

Packet "m" (Global highscore)

Packet "m" is required for displaying the global highscore

Bytes	Data type	Description
3-5	int24	snake body parts count (sct)
6-8	int24	snake last body part fullness (fam / 16777215)
9	int8	The length of the winners name
10-?	string	Winners name
?-?	string	Winners message

Snake score / length:

    Math.floor(15 * (fpsls[snake.sct] + snake.fam / fmlts[snake.sct] - 1) - 5) / 1

Packet "u" (Update minimap)

Sent when the minimap is updated.

Hints for parsing the data:

The minimap has a size of 80*80
Start at the top-left, go to the right, when at the right, repeat for the next row and so on
Start reading the packet at index 3
Read one byte:
- value >= 128: skip (value - 128) pixels
- value < 128: repeat for every bit (from the 64-bit to the 1-bit):
  - if set, paint the current pixel
  - go to the next pixel

Packet "s" (Add/remove Snake)

Variant 1: packet-size = 6

Sent when another snake leaves range (that is, close enough to be drawn on screen) or dies.

Bytes	Data type	Description
3-4	int16	Snake id
5	int8	0 (snake left range) or 1 (snake died)

Variant 2: packet-size >= 34

Sent when another snake enters range.

Bytes	Data type	Description
3-4	int16	Snake id
5-7	int24	Snake ehang / wehang (value * 2 * Math.PI / 16777215)
8	int8	Unused. The 8th byte is unused in the game code. But the Server sends it filled with a value. Maybe we miss something here?
9-11	int24	Snake angle eang / wang (value * 2 * Math.PI / 16777215)
12-13	int16	Snake speed (value / 1E3)
14-16	int24	Snake last body part fullness (fam / 16777215)
17	int8	Snake skin (between 9 or 0? and 21)
18-20	int24	value / 5 snake X pos
21-23	int24	value / 5 snake Y pos
24	int8	Name length (-> `n`)
25-(24+`n`) (`n` values)	string	Snake nickname
25+`n`	int8	Custom-skin-data-length (-> `s`)
(26+`n`)-(25+`n`+`s`) (`s` values)	bytes	Custom-skin-data
(26+`n`+`s`)-(28+`n`+`s`)	int24	Last snake body part (tail) position in absolute coords (x / 5)
(29+`n`+`s`)-(31+`n`+`s`)	int24	Last snake body part (tail) position in absolute coords (y / 5)
32+`n`+`s`	int8	Next position in relative coords from prev. element (x - 127) / 2
33+`n`+`s`	int8	Next position in relative coords from prev. element (y - 127) / 2

The last two bytes repeat for each body part.

Packet "F" (Add Food)

Sent when food that existed before enters range.

Bytes	Data type	Description
3	int8	Color?
4-5	int16	Food X
6-7	int16	Food Y
8	int8	value / 5 -> Size
One packet can contain more than one food-entity, bytes 3-8 (=6 bytes!) repeat for every entity.

The food id is calculated with (y * GameRadius * 3) + x

Packet "b" (Add Food)

Sent when food is created while in range (because of turbo or the death of a snake).

Bytes	Data type	Description
3	int8	Color?
4-5	int16	Food X
6-7	int16	Food Y
8	int8	value / 5 -> Size

The food id is calculated with (y * GameRadius * 3) + x

Packet "f" (Add Food)

Sent when natural food spawns while in range.

Bytes	Data type	Description
3	int8	Color?
4-5	int16	Food X
6-7	int16	Food Y
8	int8	value / 5 -> Size

The food id is calculated with (y * GameRadius * 3) + x

Packet "c" (Eat Food)

The food id is also calculated with (y * GameRadius * 3) + x

Bytes	Data type	Description
3-4	int16	Food X
5-6	int16	Food Y
7-8	int16	Eater snake id

The packet doesn't always contain the eater snake id, in this case the food was removed for other reasons (?).

Packet "j" (Update Prey)

Sent when prey ("flying particles") is updated.

Bytes	Data type	Description
3-4	int16	Prey ID
5-6	int16	value * 3 + 1 -> x
7-8	int16	value * 3 + 1 -> y

Next follow updates for one or more of these variables:

Data type	Description
int8	value - 48 -> direction (0: not turning; 1: turning counter-clockwise; 2: turning clockwise)
int24	value * 2 * PI / 16777215 -> current angle
int24	value * 2 * PI / 16777215 -> wanted angle (angle the prey turns towards)
int16	value / 1000 -> speed

Depending on the packet-length, different variables are sent:

packet-length	variables sent (in that exact order)
11	speed
12	current angle
13	direction, wanted angle
14	current angle, speed
15	direction, wanted angle, speed
16	direction, current angle, wanted angle
18	direction, current angle, wanted angle, speed

Packet "y" (Add/remove Prey)

Sent when a Prey enters range / spawns or leaves range / gets eaten. The exact event/format depends on the packet-length:

packet-length 5: remove Prey

Bytes	Data type	Description
3-4	int16	Prey ID

packet-length 7: eat Prey

Bytes	Data type	Description
3-4	int16	Prey ID
5-6	int16	Eater snake ID

packet-length 22: add Prey

Bytes	Data type	Description
3-4	int16	Prey ID
5	int8	color ID
6-8	int24	value / 5 -> x
9-11	int24	value / 5 -> y
12	int8	value / 5 -> size
13	int8	value - 48 -> direction (see packet "j")
14-16	int24	value * 2 * PI / 16777215 -> wanted angle
17-19	int24	value * 2 * PI / 16777215 -> current angle
20-21	int16	value / 1000 -> speed

Packet "o" (Verify code response)

Response from the server when the player entered a code via the verify code packet, potentially unlocking cosmetics. No work was put into deciphering this packet-type yet (cosmetics are only visible locally, so it is pretty boring).

Packet "k" (Kill)

Note: this packet is (currently) unused in the original client, so I can only guess what the variables mean.

Sent when another snake dies by running into the player; not sent when the killer isn't the local player.

Bytes	Data type	Description
3-4	int16	killer snake id
5-7	int24	total number of kills

Serverbound

All packets sent from the client contain no headers.

Packet StartLogin

This is the first packet sent. The server will then respond with the Pre-init response.

Byte	Data type	Description
0	int8	99 (= 'c')

Packet SetUsernameAndSkin

This packet is sent before sending the ping packet to the server. The setup packet will only be sent after receiving this and the ping packet.

Bytes	Data type	Description
0	int8	packet-type (here 115 = 's')
1	int8	Second ID (protocol_version-1, currently 10 for protocol_version 11)
2	int8	Skin ID currently between 0-38 meaning 39 skins available
3	int8	Nickname length (`n`)
4-(3+`n`) (`n` values)	string	The client's nickname, if set
(4+`n`)-?	bytes	Custom-skin-data

Packet Verify code

When you enter the username "bonkers", you can enter a 12-digit code. This code will be sent to the server for verification.

Bytes	Data type	Description
0	int8	packet-type (here 111 = 'o')
1-2	int8	first group of four digits as one number
3-4	int8	second group of four digits as one number
5-6	int8	third group of four digits as one number

Packet Ping

Pings the server. Sent every 250ms, but not before a pong has been received after the last ping.

Bytes	Data type	Description
0	int8	Value(always 251)

Packet UpdateOwnSnake

The client sends this packet to the server when it receives a mouseMove, mouseDown, mouseUp, keyDown or keyUp event.

Bytes	Data type	Value	Description
0	int8	0-250	mouseMove: the input angle. Clockwise, y-axes looks down the screen
0	int8	252	keyDown, keyUp (left-arrow or right-arrow): turning left or right
0	int8	253	mouseDown, keyDown (space or up-arrow): the snake is entering speed mode
0	int8	254	mouseUp, keyUp (space or up-arrow): the snake is leaving speed mode
1	int8	0-255	virtual (8ms) frames of counted rotation (0-127 left turns, 128-255 right turns, used when 1st byte is 252)

angle in radians = 2pi * value / 250

Packet SaveVictoryMessage

When you have the longest snake of the day, you're able to send a victory message.

Bytes	Data type	Description
0	int8	First ID (always 255)
1	int8	Second ID (always 118)
2-?	string	The victory message

Additional information

Custom-skin-data

Bytes	Description
0	Always 255
1	Always 255
2	Always 255
3	Always 0
4	Always 0
5	Always 0
6	`Math.floor(256 * Math.random())`
7	`Math.floor(256 * Math.random())`
8	Size of color-group
9	Color-id of color-group

The last two bytes repeat for each color-group, starting at the head

The first 8 bytes have no meaning, the server accepts anything here and sends that data to other players.

The own custom-skin is stored in the localStorage, key 'custom_skin' (string with comma-separated values).

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Protocol.md

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Slither.io Protocol Version 11

Clientbound

Message Types

Packet "6" (Pre-init response)

Packet "a" (Initial setup)

Packet "e" (Snake rotation counterclockwise (?dir ang ?wang ?sp))

Packet "E" (Snake rotation counterclockwise (dir wang ?sp))

Packet "3" (Snake rotation counterclockwise (dir ang wang | sp))

Packet "4" (Snake rotation clockwise (dir ang? wang ?sp))

Packet "5" (Snake rotation clockwise (dir ang wang))

Packet "h" (Update snake last body part fullness (fam))

Packet "r" (Remove snake part)

Variant 1: packet-size = 5

Variant 2: packet-size = 8

Packet "g" (Move snake)

Packet "G" (Move snake)

Packet "n" (Increase snake)

Packet "N" (Increase snake)

Packet "l" (Leaderboard)

Packet "v" (dead/disconnect packet)

Packet "W" (Add Sector)

Packet "w" (Remove Sector)

Packet "m" (Global highscore)

Packet "u" (Update minimap)

Packet "s" (Add/remove Snake)

Variant 1: packet-size = 6

Variant 2: packet-size >= 34

Packet "F" (Add Food)

Packet "b" (Add Food)

Packet "f" (Add Food)

Packet "c" (Eat Food)

Packet "j" (Update Prey)

Packet "y" (Add/remove Prey)

packet-length 5: remove Prey

packet-length 7: eat Prey

packet-length 22: add Prey

Packet "o" (Verify code response)

Packet "k" (Kill)

Serverbound

Packet StartLogin

Packet SetUsernameAndSkin

Packet Verify code

Packet Ping

Packet UpdateOwnSnake

Packet SaveVictoryMessage

Additional information

Custom-skin-data