The MathJSON Format
The MathJSON format is a lightweight data interchange format for mathematical notation.
It is humanreadable, while being easy for machines to generate and parse.
It is built on the JSON [1] format. Its focus is on interoperability between software programs to facilitate the exchange of mathematical data, as well as the building of complex software through the integration of software components communicating with a common format.
It is not suitable as a visual representation of arbitrary mathematical notations, and as such is not a replacement for LaTeX or MathML.
Examples
Euler's Identity
In TeX
e^{\imaginaryI \pi }+1=0
In MathJSON:
{
"fn":"equal",
"arg":[{
"fn":"add",
"arg":[{
"sym":"e",
"sup":{
"fn":"multiply",
"arg":[{"sym": "ⅈ"},{sym:"π"}]
}
},
{"num": "1"}
]
},
"num": "0"
]
}
An approximation of Pi
\frac {63}{25}\times \frac {17+15\sqrt{5}}{7+15\sqrt{5}}
{"fn":"multiply",
"arg":[
{"fn":"divide","arg":[{"num":"63"},{"num":"25"}]},
{"fn":"divide","arg":[
{"fn":"add","arg":[
{"num":"17"},
{"fn":"multiply","arg":[{"num":"15"},{"fn":"sqrt","arg":[{"num":"5"}]}]}
]},
{"fn":"add","arg":[
{"num":"7"},
{"fn":"multiply","arg":[
{"num":"15"},
{"fn":"sqrt","arg":[
{"num":"5"}
]}
]}
]}
]}
]
}
Design Goals
Definitions
 producer software that generates a MathJSON data structure
 consumer software that parses and acts on a MathJSON data structure
Goals
 Easy to consume, even if that's at the expense of complexity to generate.
 Extensibility. It should be possible to add information to the data structure that can help its interpretation or its rendition. This information should be optional and can be ignored by any consumer.
Nongoals
 Be suitable as an internal data structure
 Be suitable as a display format
 Capture complete semantic information with no ambiguity and in a selfsufficient manner.
Encoding
A MathJSON expression is an abstract syntax tree encoded as a JSON object.
The root element is an expression
, with child nodes according
to the grammar below.
Basic Number
A basic number is encoded following the JSON grammar, with the following extensions:
 support for arbitrary precision numbers. JavaScript and many other languages only support limited precision numbers, generally 52bit integers (about 15 digits). Therefore to support arbitrary precision, numbers should always be represented as a quoted string.
 support for
NaN
andinfinity
basicnumber
:= '"NaN"'
 infinity
 '"'
[''
] int
[ frac
] [ exp
]'"'
infinity
:= '"'
['+'
 ''
] 'Infinity'
'"'
int
:= '0'
 [ '0'
 '9'
]*
frac
:= '.'
('0'
 '9'
)*
exp
:= ['e'
 'E'
] ['+'
 ''
] ('0'
 '9'
)*
Native Strings
Native strings are a sequence of Unicode characters.
MATSON producing software should not generate character entities in strings.
As per JSON, any Unicode character may be escaped using a \u
escape sequence.
Whenever applicable, a specific Unicode symbol should be used.
For example, the set of complex numbers should be represented with U+2102 ℂ, not with U+0043 C and a math variant styling attribute.
See Unicode Chapter 22  Symbols
When used with markup languages—for example, with Mathematical Markup Language (MathML)—the characters are expected to be used directly, instead of indirectly via entity references or by composing them from base letters and style markup.
Optional keys
All nodes may have the following keys:
sub
:expression
, a subscriptsup
:expression
, a superscriptcomment
: A human readable string to annotate an expression, since JSON does not allow comments in its encodingerror
: A human readable string that can be used to indicate a syntax error or other problem when parsing or evaluating an expression.latex
: A visual representation in LaTeX of the expression. This can be useful to preserve nonsemantic details, for example parentheses in an expression or styling attributes.mathml
: A visual representation in MathML of the expression.class
: A CSS class to be associated with a representation of this nodeid
: A CSS id to be associated with a representation of this nodestyle
: A CSS style stringwikidata
: A short string indicating an entry in a wikibase. For example,"Q2111"
wikibase
: A base URL for the wikidata key. A full URL can be produced by concatenating this key with the wikidata key. This key applies to this node and all its children. The default value is "https://www.wikidata.org/wiki/"openmathcd
: A base URL for an OpenMath content dictionary. This key applies to this node and all its children. The default value is "http://www.openmath.org/cd".openmathsymbol
: A short string indicating an entry in an OpenMath Content Dictionary. For example:arith1/#abs
.
Key order
The order of the keys in a node is not significant.
All these expressions are equivalent:
{"fn":"add", "arg":[{num:"1"}, {num:"2"}]}
{"arg":[{num:"1"}, {num:"2"}], "fn":"add"}
However, the order of the elements in an array is significant.
These two expressions are not equivalent:
{"fn":"divide", "arg":[{num:"3"}, {num:"1"}]}
{"fn":"divide", "arg":[{num:"3"}, {num:"1"}]}
Grammar
An expression is an Abstract Syntax Tree. As such, there is no need to introduce parentheses or to resort to operator precedence in order to parse the expression correctly.
The type of each node is indicated by the presence of a specific key, for example sym
for the "symbol" node or fn
for the "function" node.
There are five types of nodes:
expression
:= number

symbol

function

group

text

number
A node with the following key:
num
:basicnumber
complexnumber
complexnumber
:= { "re": basicnumber
, "im": basicnumber
}
symbol
A node with the following keys
sym
:nativestring
type
: nativestring`, the data type of the symbol. See table below.index
: A 0based index into a vector or array. An index can be a number or an array of numbers.accent
:string
, a modifier applied to a symbol, such as "hat" or "bar".
The sym
key is the only required key.
Type
The data type of a symbol can be used to refine the interpretation of operations performed upon it.
Data Type  Value  Meanings 

Scalar  scalar 
scalar number 
Complex  complex 
complex number 
Vector  vector 
an element composed of n scalars or complex numbers 
Matrix  matrix 
an element composed of n vectors 
Function  function 

String  string 
an array of characters 
Dictionary  dictionary 
a collection of key/value pairs 
Boolean  boolean 
true or false 
Table  table 
a twodimensional array of cells. Each cell can be of a different type. 
Date  date 

Duration  duration 
Accent
An accent is a decoration over a symbol that provides the proper context to interpret the symbol or modifies it in some way. For example, an accent can indicate that a symbol is a vector, or to represent the mean, complex conjugate or complement of the symbol.
The following values are recommended:
Accent  Value  Unicode  Possible Meanings 

Vector  ◌⃗  U+20d7  
Bar  ◌¯  U+00af  Mean, complex conjugate, set complement. 
Hat  ◌^  U+005e  Unit vector, estimator 
Dot  ◌˙  U+02d9  Derivative with respect to time 
Double dot  ◌¨  U+00a8  Second derivative with respect to time. 
Acute  ◌´  U+00b4  
Grave  ◌`  U+0060  
Tilde  ◌~  U+007e  
Breve  ◌˘  U+02d8  
Check  ◌ˇ  U+02c7 
function
fn
:nativestring
, the name of the function.arg
: array ofexpression
, the arguments to the function.fence
:string
, one to three characters indicating the delimiters used for the expression. The first character is the opening delimiter, the second character, if present, is the closing delimiter. The third character, if present, is the delimiters separating the arguments. If no value is provided for this key, the default value(),
is used. The character.
can be used to indicate the absence of a delimiter, for example..;
.sub
:expression
sup
:expression
accent
:nativestring
, a single unicode character representing the accent to display over the function. See the SYMBOL section for more details.
The fn
key is the only required key.
When using common functions, the following values are recommended:
Name (and common synonyms)  Arity  Comment 

add 
2+  
multiply 
2+  
subtract 
2  Subtract the second from the first. 
divide 
2  The first argument divided by the second argument 
negate 
1  Negate the argument 
list 
1+  comma separated list 
list2 
1+  semicolon separated list 
Name (and common synonyms)  Arity  Comment 

Signum  1  1 if the argument is negative, 0 if it is zero, 1 if it is positive; more generally, the intersection of the unit circle with the line from the origin through the argument in the complex plane 
Exponential  1  e to the power of the argument. 
Power  2  The first argument to the power of the second argument 
Square Root  1  
Root  2  The second argument is the degree of the root 
Natural log  1  
Logarithm  2  The second argument is the base. 
abs 
1  Absolute value 
min 
2, n  The smallest of the arguments 
max 
2, n  The largest of the arguments 
floor 
1  The largest integer less than or equal to the argument 
ceiling 
1  The smallest integer greater than or equal to the argument 
gcd 
2  Greatest Common Divisor 
lcm 
2  Least Common Multiple 
compose 
2, n 
Complex Arithmetic
Name  Value  Arity  Comment 

Conjugate  + 
1  Conjugate of the argument 
Real  real 
1  
Imaginary  imaginary 
1  
Argument  arg 
1 
Logic
Name  Value  Arity  Comment 

Implies  
Logical equivalence  
For All (universal quantifier)  forall 

There Exists (existential quantifier)  exists 
There Does Not Exists
Trigonometry
Note that for inverse functions, no assumptions is made about the branch cuts of those functions. The interpretation is left up to the consuming software.
Name (and common synonyms)  Value  Arity  Comment 

Cosine  cos 
1  angle in radians 
Sin  sin 
1  angle in radians 
Tangent (tan, tg)  tan 
1  angle in radians 
Cotangent (cot, ctg, cotg, ctn)  cotangent 
1  
Secant  sec 
1  
Cosecant  csc 
1  
Arc cosine  acos 
1  angle in radians 
Arc sine  asin 
1  angle in radians 
Arctangent (arctan, arctg)  atan 
1  angle in radians 
Arctangent (arctan, arctg)  atan 
2  See https://en.wikipedia.org/wiki/Atan2 
Arccotangent  arccot 
1  
Arcsecant  arcsec 
1  
Arccosecant  arccsc 
1  
Hyperbolic tangent (th, tan)  tanh 
1 
Relational operators
Operation  Value  Comment 

Equal to  equal 
General purpose equality 
Less than  lt 

Less than or equal to  le 

Greater than  gt 

Greater than or equal to  ge 

Much less than  ll 
x ≪ y 
Much greater than  gg 
y ≫ x 
Definition/assignment  assign 
Used with a := 5 or f(x) := sin(x) 
Identity  :=: 
Used with 1 + 1 :=: 2 
Approximately equal to  approx 
Used with π ≈ 3.14 
Not equal to  ne 

Similar to  sim 
2 ~ 5 
Congruent to  cong 
A ≅ B 
There are three semantically distinct use for "equal to" which are often all represented with =
in mathematical notation:
 conditional equality: the expression is true when the left hand side and the right hand side are equal, for example when defining a curve representing the unit circle:
x^2 + y^2 = 1
 definition or assignment: the symbol (or expression) on the left hand side is defined by the expression on the right hand side. For example
f(x) := sin x
,a := 5
 identity: the right hand side expression is a syntactic derivation from the left hand size expression. For example,
1 + 1 :=: 2
When a more specific version cannot be determined from the context, the
general purpose equal
function should be used.
Big operators
Big operators, such as ∑, "sum", and ∏, "product", are represented as a function with the following arguments:
 first argument: body of the operation
 second argument (optional): inferior argument of the operation
 third argument (optional): superior argument of the operation
For example:
\sum ^n_{i=0}i
{
"fn":"sum",
"arg":[
{sym: "i"},
{"fn":"=","arg":["i", 0]},
{sym: "n"}
]
}
If necessary, an empty argument can be represented by an empty structure.
The following values should be used to represent these common big operators:
Operation  Value  Comment 

Sum  sum 
∑ U+2211 
Product  product 
∏ U+220f 
Intersection  intersection 
⋂ U+22c2 
Union  union 
⋃ U+22c3 
Integral  integral 
∫ U+222b 
Double integral  integral2 
∬ U+222c 
Triple integral  integral3 
∭ U+222d 
Contour integral  contour_integral 
∮ U+222e 
Circle Plus  circle_plus 
U+2a01 
Circle Times  circle_times 
U+2a02 
And  n_and 
U+22c1 
Or  n_or 
U+22c0 
Coproduct  coproduct 
∐ U+2210 
Square cup  square_cup 
U+2a06 
U plus  union_plus 
U+2a04 
O dot  odot 
U+2a00 
Special Functions
These functions represent higher order data structures and operations common in algebraic manipulation systems.
 bind first argument is an expression, argument 2n is an identifier, argument 2n+1 is the value the identifier should be replaced with.
Argument 2n+1 can be a number, an expression, an array representing a list of values, or a range. If an array or a range, the result is an array of expression.
For example:
{ "fn":"bind",
"arg": [
{"fn":"+","arg":[{"sym":"x","sup":2},{"fn":"*","arg":[2,"x"]}]},
"x",
"1"
]
}
would replace the x
in the expression with 1
.

solve first argument is an expression. Return an array of identifier and their value. The first argument can be an array representing a system of equations.

range first argument is the start of the range, second argument is the end of the third. The third argument is optional and represent the step between elements of the range. If none is provided, the step is 1.

block
the arguments are a list of expressions, such as in a system of equations. 
case
the arguments are a list of conditional expressions, such as in a piecewise definition of a function. Arguments 2n1 are the expression, and 2n are the condition. The last condition is optional and the last value is applied if no other condition match.
Other functions
Operation  Value  Comment 

Factorial  factorial 
! 
Double factorial  factorial2 
!! 
Additional functions can be specified using an OpenMath content dictionary. For example, Euler's gamma function:
{
fn: "gamma",
openmathsymbol: "hypergeo0#gamma",
arg: 1
}
If an openmathsymbol
key is present it overrides the value of the fn
key as far as the semantic of the operation is concerned. However, the fn
key can still be used to display information about this expression to a user. For example:
{
fn: "\u0393",
openmathsymbol: "hypergeo0#gamma",
arg: 1
}
where \u0393
is the Unicode character GREEK CAPITAL LETTER GAMMA
Γ.
group
group
:expression
sup
:expression
sub
:expression
accent
:string
The group
key is the only one required.
This element is used when a sup
, sub
or accent
needs to be applied to an expression, as in (x+1)^2
.
text
text
:nativestring
format
: "plain"  "markdown"  "html". This key is optional and its default value isplain
The text
key is the only one required.
OPEN QUESTIONS
 How should exponents be represented? I.e.
x^2
orA^\dagger
. They could literally be represented with asup
attribute, or as an explicit function, i.e.fn:'pow'
orfn:'transjugate'
 Clarify how to represent variants for multiplications, e.g.
a \times b
,a . b
,a * b
,ab
, etc...  How to encode logarithm and exponential (see 1.)
 What should the effect of nary versions of divide, substract? One option is to apply a leftreduce to the arguments.
 How should accents (i.e. arrow over symbol) be encoded? As an additional property? As a function? How about other stylistic variant (i.e. bold symbol, fraktur, blackboard, etc...)
 Should there be a node type to represent conditions, i.e. expressions whose value is a boolean.
 For functions defined with an openmath identifier, the value of the
fn
key could be the openmath identifier, i.e.fn:"hypergeo0#gamma"
REFERENCES
 https://www.json.org/
 http://www.openmath.org/cd