]> Fachhochschule Dortmund

Sonnenstraße 96 Dortmund D-44139 Germany stefan.goessner@fh-dortmund.de

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Universität Bremen TZI

Postfach 330440 Bremen D-28359 Germany +49-421-218-63921 cabo@tzi.org

ART JSONPath WG JSON JSONPath defines a string syntax for selecting and extracting values within a JavaScript Object Notation (JSON, RFC 8259) value. About This Document Status information for this document may be found at . Discussion of this document takes place on the JSON Path Working Group mailing list (), which is archived at . Source for this draft and an issue tracker can be found at .

Introduction JavaScript Object Notation (JSON, ) is a popular representation format for structured data values. JSONPath defines a string syntax for identifying values within a JSON value. JSONPath is not intended as a replacement for, but as a more powerful companion to, JSON Pointer . See .

Terminology The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 when, and only when, they appear in all capitals, as shown here. The grammatical rules in this document are to be interpreted as ABNF, as described in . ABNF terminal values in this document define Unicode code points rather than their UTF-8 encoding. For example, the Unicode PLACE OF INTEREST SIGN (U+2318) would be defined in ABNF as %x2318. The terminology of applies except where clarified below. The terms "Primitive" and "Structured" are used to group the types as in . Definitions for "Object", "Array", "Number", and "String" remain unchanged. Importantly "object" and "array" in particular do not take on a generic meaning, such as they would in a general programming context. Additional terms used in this specification are defined below.

Value:

As per , a structure complying to the generic data model of JSON, i.e., composed of components such as structured values, namely JSON objects and arrays, and primitive data, namely numbers and text strings as well as the special values null, true, and false.

Member:

A name/value pair in an object. (Not itself a value.)

Name:

The name in a name/value pair constituting a member. (Also known as "key", "tag", or "label".) This is also used in , but that specification does not formally define it. It is included here for completeness.

Element:

A value in an array. (Not to be confused with XML element.)

Index:

A non-negative integer that identifies a specific element in an array. Note that the term indexing is also used for accessing elements using negative integers (), and for accessing member values in an object using their member name.

Query:

Short name for JSONPath expression.

Argument:

Short name for the value a JSONPath expression is applied to.

Node:

The pair of a value along with its location within the argument.

Root Node:

The unique node whose value is the entire argument.

Children (of a node):

If the node is an array, each of its elements, or if the node is an object, each its member values (but not its member names).

Descendants (of a node):

The node itself, plus the descendants of each of its children. Note that this is often more selectively called descendant-or-self. Should we define descendants non-inclusive of the node itself? We do have the language to say "node + descendants" in several places.

Nodelist:

A list of nodes. The output of applying a query to an argument is manifested as a list of nodes. While this list can be represented in JSON, e.g. as an array, the nodelist is an abstract concept unrelated to JSON values.

Normalized Path:

A simple form of JSONPath expression that identifies a node by providing a query that results in exactly that node. Similar to, but syntactically different from, a JSON Pointer .

For the purposes of this specification, a value as defined by is also viewed as a tree of nodes. Each node, in turn, holds a value. Further nodes within each value are the elements of arrays and the member values of objects and are themselves values. (The type of the value held by a node may also be referred to as the type of the node.) A query is applied to an argument, and the output is a nodelist.

History This document picks up Stefan Goessner's popular JSONPath proposal dated 2007-02-21 and provides a normative definition for it. describes how JSONPath was inspired by XML's XPath . JSONPath was intended as a light-weight companion to JSON implementations on platforms such as PHP and JavaScript, so instead of defining its own expression language like XPath did, JSONPath delegated this to the expression language of the platform. While the languages in which JSONPath is used do have significant commonalities, over time this caused non-portability of JSONPath expressions between the ensuing platform-specific dialects. The present specification intends to remove platform dependencies and serve as a common JSONPath specification that can be used across platforms. Obviously, this means that backwards compatibility could not always be achieved; a design principle of this specification is to go with a "consensus" between implementations even if it is rough, as long as that does not jeopardize the objective of obtaining a usable, stable JSON query language.

Overview of JSONPath Expressions JSONPath expressions are applied to a JSON value, the argument. Within the JSONPath expression, the abstract name $ is used to refer to the root node of the argument, i.e., to the argument as a whole. JSONPath expressions can use the dot notation or the more general bracket notation to build paths that are input to a JSONPath implementation. JSONPath allows the wildcard symbol * to select any member of an object or any element of an array (). The descendant operator .. selects the node and all its descendants (). The array slice syntax [start:end:step] allows selecting a regular selection of an element from an array, giving a start position, an end position, and possibly a step value that moves the position from the start to the end (). Filter expressions are supported via the syntax ?(<boolean expr>) as in provides a quick overview of the JSONPath syntax elements. Overview over JSONPath

JSONPath	Description
$	the root node
@	the current node
. or []	child operator
n/a	parent operator
..	nested descendants
*	wildcard: all member values/array elements regardless of their names/indices
[]	subscript operator: index current node as an array (from 0)
[,]	list operator: allows combining member names, array indices, and slices
[start:end:step]	array slice operator
?()	applies a filter expression
()	expression, e.g., for indexing

JSONPath Examples This section provides some more examples for JSONPath expressions. The examples are based on the simple JSON value shown in , which was patterned after a typical XML example representing a bookstore (that also has bicycles).

Example JSON value

The examples in use the expression mechanism to obtain the number of elements in an array, to test for the presence of a member in a object, and to perform numeric comparisons of member values with a constant. Example JSONPath expressions applied to the example JSON value

JSONPath	Result
$.store.book[*].author	the authors of all books in the store
$..author	all authors
$.store.*	all things in store, which are some books and a red bicycle
$.store..price	the prices of everything in the store
$..book[2]	the third book
$..book[-1]	the last book in order
$..book[0,1] $..book[:2]	the first two books
$..book[?(@.isbn)]	filter all books with isbn number
$..book[?(@.price<10)]	filter all books cheaper than 10
$..*	all elements in XML document; all member values and array elements contained in input value

JSONPath Syntax and Semantics

Overview A JSONPath query is a string which selects zero or more nodes of a piece of JSON. A query MUST be encoded using UTF-8. The grammar for queries given in this document assumes that its UTF-8 form is first decoded into Unicode code points as described in ; implementation approaches that lead to an equivalent result are possible. A string to be used as a JSONPath query needs to be well-formed and valid. A string is a well-formed JSONPath query if it conforms to the ABNF syntax in this document. A well-formed JSONPath query is valid if it also fulfills all semantic requirements posed by this document. To be valid, integer numbers in the JSONPath query that are relevant to the JSONPath processing (e.g., index values and steps) MUST be within the range of exact values defined in I-JSON , namely within the interval [-(2⁵³)+1, (2⁵³)-1]). To be valid, strings on the right hand side of the =~ regex matching operator need to conform to . The well-formedness and the validity of JSONPath queries are independent of the JSON value the query is applied to; no further errors can be raised during application of the query to a value. Obviously, an implementation can still fail when executing a JSONPath query, e.g., because of resource depletion, but this is not modeled in the present specification. However, the implementation MUST NOT silently malfunction. Specifically, if a valid JSONPath query is evaluated against a structured value whose size doesn't fit in the range of exact values, interfering with the correct interpretation of the query, the implementation MUST provide an indication of overflow. (Readers familiar with the HTTP error model may be reminded of 400 type errors when pondering well-formedness and validity, while resource depletion and related errors are comparable to 500 type errors.)

Processing Model In this specification, the semantics of a JSONPath query are defined in terms of a processing model. That model is not prescriptive of the internal workings of an implementation: Implementations may wish (or need) to design a different process that yields results that are consistent with this model. In the processing model, a valid query is executed against a value, the argument, and produces a list of zero or more nodes of the value. The query is a sequence of zero or more selectors, each of which is applied to the result of the previous selector and provides input to the next selector. These results and inputs take the form of a nodelist, i.e., a sequence of zero or more nodes. The nodelist going into the first selector contains a single node, the argument. The nodelist resulting from the last selector is presented as the result of the query; depending on the specific API, it might be presented as an array of the JSON values at the nodes, an array of Normalized Paths referencing the nodes, or both -- or some other representation as desired by the implementation. Note that the API must be capable of presenting an empty nodelist as the result of the query. A selector performs its function on each of the nodes in its input nodelist, during such a function execution, such a node is referred to as the "current node". Each of these function executions produces a nodelist, which are then concatenated into the result of the selector. The processing within a selector may execute nested queries, which are in turn handled with the processing model defined here. Typically, the argument to that query will be the current node of the selector or a set of nodes subordinate to that current node.

Syntax Syntactically, a JSONPath query consists of a root selector ($), which stands for a nodelist that contains the root node of the argument, followed by a possibly empty sequence of selectors. The syntax and semantics of each selector is defined below.

Semantics The root selector $ not only selects the root node of the argument, but it also produces as output a list consisting of one node: the argument itself. A selector may select zero or more nodes for further processing. A syntactically valid selector MUST NOT produce errors. This means that some operations that might be considered erroneous, such as indexing beyond the end of an array, simply result in fewer nodes being selected. But a selector doesn't just act on a single node: a selector acts on each of the nodes in its input nodelist and concatenates the resultant nodelists to form the result nodelist of the selector. For each node in the list, the selector selects zero or more nodes, each of which is a descendant of the node or the node itself. For instance, with the argument {"a":[{"b":0},{"b":1},{"c":2}]}, the query $.a[*].b selects the following list of nodes: 0, 1 (denoted here by their value). Let's walk through this in detail. The query consists of $ followed by three selectors: .a, [*], and .b. Firstly, $ selects the root node which is the argument. So the result is a list consisting of just the root node. Next, .a selects from any input node of type object and selects the node of any member value of the input node corresponding to the member name "a". The result is again a list of one node: [{"b":0},{"b":1},{"c":2}]. Next, [*] selects from an input node of type array all its elements (if the input note were of type object, it would select all its member values, but not the member names). The result is a list of three nodes: {"b":0}, {"b":1}, and {"c":2}. Finally, .b selects from any input node of type object with a member name b and selects the node of the member value of the input node corresponding to that name. The result is a list containing 0, 1. This is the concatenation of three lists, two of length one containing 0, 1, respectively, and one of length zero. As a consequence of this approach, if any of the selectors selects no nodes, then the whole query selects no nodes. In what follows, the semantics of each selector are defined for each type of node.

Selectors A JSONPath query consists of a sequence of selectors. Valid selectors are

• Root selector $ (used at the start of a query and in expressions)
• Dot selector .<name>, used with object member names exclusively.
• Dot wild card selector .*.
• Index selector [<index>], where <index> is either a (possibly negative, see ) array index or an object member name.
• Index wild card selector [*].
• Array slice selector [<start>:<end>:<step>], where the optional values <start>, <end>, and <step> are integer literals.
• Nested descendants selector ...
• List selector [<sel1>,<sel2>,...,<selN>], holding a comma separated list of index and slice selectors.
• Filter selector [?(<expr>)]
• Current item selector @ (used in expressions)

Root Selector

Syntax Every valid JSONPath query MUST begin with the root selector $.

Semantics The Argument -- the root JSON value -- becomes the root node, which is addressed by the root selector $.

Dot Selector

Syntax A dot selector starts with a dot . followed by an object's member name. Member names containing characters other than allowed by dot-selector -- such as space ` , minus -, or dot . characters -- MUST NOT be used with the dot-selector. (Such member names can be addressed by the index-selector` instead.)

Semantics The dot-selector selects the node of the member value corresponding to the member name from any JSON object in its input nodelist. It selects no nodes from any other JSON value.

Dot Wild Card Selector

Syntax The dot wild card selector has the form .* as defined in the following syntax:

Semantics A dot-wild-selector acts as a wild card by selecting the nodes of all member values of an object in its input nodelist as well as all element nodes of an array in its input nodelist. Applying the dot-wild-selector to a primitive JSON value (number, string, or true/false/null) selects no node.

Index Selector

Syntax An index selector [<index>] addresses at most one object member value or at most one array element value. Applying the index-selector to an object value in its input nodelist, a quoted-member-name string is required to select the corresponding member value. In contrast to JSON, the JSONPath syntax allows strings to be enclosed in single or double quotes. Applying the index-selector to an array, a numerical element-index is required to select the corresponding element. JSONPath allows it to be negative (see ). Notes: 1. double-quoted strings follow the JSON string syntax (); single-quoted strings follow an analogous pattern (). 2. An element-index is an integer (in base 10, as in JSON numbers). 3. As in JSON numbers, the syntax does not allow octal-like integers with leading zeros such as 01 or -01.

Semantics A quoted-member-name string MUST be converted to a member name by removing the surrounding quotes and replacing each escape sequence with its equivalent Unicode character, as in the table below: Escape Sequence Replacements

Escape Sequence	Unicode Character	Description
\b	U+0008	BS backspace
\t	U+0009	HT horizontal tab
\n	U+000A	LF line feed
\f	U+000C	FF form feed
\r	U+000D	CR carriage return
\"	U+0022	quotation mark
\'	U+0027	apostrophe
\/	U+002F	slash (solidus)
\\	U+005C	backslash (reverse solidus)
\uXXXX	U+XXXX	unicode character

The index-selector applied with a quoted-member-name to an object selects the node of the corresponding member value from it, if and only if that object has a member with that name. Nothing is selected from a value that is not a object. Array indexing via element-index is a way of selecting a particular array element using a zero-based index. For example, selector [0] selects the first and selector [4] the fifth element of a sufficiently long array. A negative element-index counts from the array end. For example, selector [-1] selects the last and selector [-2] selects the penultimate element of an array with at least two elements. As with non-negative indexes, it is not an error if such an element does not exist; this simply means that no element is selected.

Index Wild Card Selector

Syntax The index wild card selector has the form [*].

Semantics An index-wild-selector selects the nodes of all member values of an object as well as of all elements of an array. Applying the index-wild-selector to a primitive JSON value (such as a number, string, or true/false/null) selects no node. The index-wild-selector behaves identically to the dot-wild-selector.

Array Slice Selector

Syntax The array slice selector has the form [<start>:<end>:<step>]. It selects elements starting at index <start>, ending at -- but not including -- <end>, while incrementing by step. The slice-selector consists of three optional decimal integers separated by colons.

Semantics The slice-selector was inspired by the slice operator of ECMAScript 4 (ES4), which was deprecated in 2014, and that of Python.

Informal Introduction This section is non-normative. Array indexing is a way of selecting a particular element of an array using a 0-based index. For example, the expression [0] selects the first element of a non-empty array. Negative indices index from the end of an array. For example, the expression [-2] selects the last but one element of an array with at least two elements. Array slicing is inspired by the behaviour of the Array.prototype.slice method of the JavaScript language as defined by the ECMA-262 standard , with the addition of the step parameter, which is inspired by the Python slice expression. The array slice expression [start:end:step] selects elements at indices starting at start, incrementing by step, and ending with end (which is itself excluded). So, for example, the expression [1:3] (where step defaults to 1) selects elements with indices 1 and 2 (in that order) whereas [1:5:2] selects elements with indices 1 and 3. When step is negative, elements are selected in reverse order. Thus, for example, [5:1:-2] selects elements with indices 5 and 3, in that order and [::-1] selects all the elements of an array in reverse order. When step is 0, no elements are selected. (This is the one case that differs from the behaviour of Python, which raises an error in this case.) The following section specifies the behaviour fully, without depending on JavaScript or Python behaviour.

Detailed Semantics An array selector is either an array slice or an array index, which is defined in terms of an array slice. A slice expression selects a subset of the elements of the input array, in the same order as the array or the reverse order, depending on the sign of the step parameter. It selects no nodes from a node that is not an array. A slice is defined by the two slice parameters, start and end, and an iteration delta, step. Each of these parameters is optional. len is the length of the input array. The default value for step is 1. The default values for start and end depend on the sign of step, as follows: Default array slice start and end values

Condition	start	end
step >= 0	0	len
step < 0	len - 1	-len - 1

Slice expression parameters start and end are not directly usable as slice bounds and must first be normalized. Normalization for this purpose is defined as: = 0 THEN RETURN i ELSE RETURN len + i END IF ]]> The result of the array indexing expression [i] applied to an array of length len is defined to be the result of the array slicing expression [i:Normalize(i, len)+1:1]. Slice expression parameters start and end are used to derive slice bounds lower and upper. The direction of the iteration, defined by the sign of step, determines which of the parameters is the lower bound and which is the upper bound: = 0 THEN lower = MIN(MAX(n_start, 0), len) upper = MIN(MAX(n_end, 0), len) ELSE upper = MIN(MAX(n_start, -1), len-1) lower = MIN(MAX(n_end, -1), len-1) END IF RETURN (lower, upper) ]]> The slice expression selects elements with indices between the lower and upper bounds. In the following pseudocode, the a(i) construct expresses the 0-based indexing operation on the underlying array. 0 THEN i = lower WHILE i < upper: SELECT a(i) i = i + step END WHILE ELSE if step < 0 THEN i = upper WHILE lower < i: SELECT a(i) i = i + step END WHILE END IF ]]> When step = 0, no elements are selected and the result array is empty. To be valid, the slice expression parameters MUST be in the I-JSON range of exact values, see .

Descendant Selector

Syntax The descendant selector starts with a double dot .. and can be followed by an object member name (similar to the dot-selector), by an index-selector acting on objects or arrays, or by a wild card. index-selector / ; ..[] index-wild-selector / ; ..[*] "*" ; ..* ) ]]>

Semantics The descendant-selector selects the node and all its descendants. In the resultant nodelist: * nodes occur before their children, and * nodes of an array occur in array order. Children of an object may occur in any order, since JSON objects are unordered.

List Selector The list selector allows combining member names, array indices, and slices in a single selector. Note: The list selector was called "union selector" in , as it was intended to solve use cases addressed by the union selector in XPath. However, the term "union" has the connotation of a set operation that involves merging input sets while avoiding duplicates, so the concept was renamed into "list selector".

Syntax The list selector is syntactically related to the index-selector and the slice-selector. It contains two or more entries, separated by commas.

Semantics A list selector selects the nodes that are selected by at least one of the selector entries in the list and yields the concatenation of the lists (in the order of the selector entries) of nodes selected by the selector entries. Note that any node selected in more than one of the selector entries is kept as many times in the node list. To be valid, integer values in the element-index and slice-index components MUST be in the I-JSON range of exact values, see .

Filter Selector

Syntax The filter selector has the form [?<expr>]. It works via iterating over structured values, i.e. arrays and objects. During iteration process each array element or object member is visited and its value -- accessible via symbol @ -- or one of its descendants -- uniquely defined by a relative path -- is tested against a boolean expression boolean-expr. The current item is selected if and only if the result is true. " / ; operators "<=" / ">=" number = int [ frac ] [ exp ] ; decimal number frac = "." 1*DIGIT ; decimal fraction exp = "e" [ "-" / "+" ] 1*DIGIT ; decimal exponent true = %x74.72.75.65 ; true false = %x66.61.6c.73.65 ; false null = %x6e.75.6c.6c ; null regex-expr = (path / string-literal) S regex-op S regex regex-op = "=~" ; regular expression match regex = string-literal ; I-Regexp ]]> Notes:

• Parentheses can be used with boolean-expr for grouping. So filter selection syntax in the original proposal [?(<expr>)] is naturally contained in the current lean syntax [?<expr>] as a special case.
• Comparisons are restricted to primitive values (such as number, string, true, false, null). Comparisons with complex values will fail, i.e. no selection occurs.
• Data types are not implicitly converted in comparisons. So "13 == '13'" selects no node.
• A member or element value by itself in a Boolean context is interpreted as false only if it does not exist. Otherwise it is interpreted as true. To be more specific about the actual value, explicit comparisons are necessary. This existence test -- as an exception to the general rule -- also works with structured values.
• The regular expressions in the string-literals on the right-hand side of =~ are as defined in . Regular expression tests can be applied to JSON string values () only (on the left-hand side of =~); they yield false otherwise.
• Alphabetic characters in ABNF are case-insensitive, so "e" can be either "e" or "E".
• false, null, true are lower-case only (case-sensitive).

The following table lists filter expression operators in order of precedence from highest (binds most tightly) to lowest (binds least tightly). Filter expression operator precedence

Precedence	Operator type	Syntax
5	Grouping	(...)
4	Logical NOT	!
3	Relations	== != < <= > >= =~ in
2	Logical AND	&&
1	Logical OR	||

Semantics The filter-selector works with arrays and objects exclusively. Its result might be a list of zero, one, multiple or all of their element or member values then. Applied to other value types, it will select nothing. Some examples:

JSON	Query	Result	Comment
{"a":1,"b":2} [2,3,4]	$[?@]	[1,2] [2,3,4]	Same as $.* or $[*]
./.	$[?@==2]	[2] [2]	Select by value.
{"a":{"b":{"c":{}}}	$[?@.b] $[?@.b.c]	[{"b":{"c":{}}]	Existence
{"key":false}	$[?index(@)=='key'] $[?index(@)==0]	[false] []	Select object member
[3,4,5]	$[?index(@)==2] $[?index(@)==17]	[5] []	Select array element
{"a":{"b":{5},c:0}}	$[?@.b==5 && !@.c]	[{"b":{5},c:0}]	Existence

Normalized Paths A Normalized Path is a JSONPath with restricted syntax that identifies a node by providing a query that results in exactly that node. For example, the JSONPath expression $.book[?(@.price<10)] could select two values with Normalized Paths $['book'][3] and $['book'][5]. For a given JSON document, there is a one to one correspondence between the document's nodes and the Normalized Paths that identify these nodes. A JSONPath implementation may output Normalized Paths instead of, or in addition to, the values identified by these paths. Since bracket notation is more general than dot notation, it is used to construct Normalized Paths. Single quotes are used to delimit string member names. This reduces the number of characters that need escaping when Normalized Paths appear as strings (which are delimited with double quotes) in JSON documents. The syntax of Normalized Paths is restricted so that there is one and only one way of representing any given Normalized Path. Putting this another way, for any two distinct Normalized Paths, a JSON document exists that will yield distinct results when the Normalized Paths are applied to it. Certain characters are escaped, in one and only one way; all other characters are unescaped.

IANA Considerations

Registration of Media Type application/jsonpath IANA is requested to register the following media type :

Type name:

application

Subtype name:

jsonpath

Required parameters:

N/A

Optional parameters:

N/A

Encoding considerations:

binary (UTF-8)

Security considerations:

See the Security Considerations section of RFCXXXX.

Interoperability considerations:

N/A

Published specification:

RFCXXXX

Applications that use this media type:

Applications that need to convey queries in JSON data

Fragment identifier considerations:

N/A

Additional information:

Deprecated alias names for this type:

N/A

Magic number(s):

N/A

File extension(s):

N/A

Macintosh file type code(s):

N/A

Person & email address to contact for further information: iesg@ietf.org

Intended usage:

COMMON

Restrictions on usage:

N/A

Author:

JSONPath WG

Change controller:

IESG

Provisional registration? (standards tree only):

no

Security Considerations This section gives security considerations, as required by .

References Normative References ISO/IEC 10646-1 defines a large character set called the Universal Character Set (UCS) which encompasses most of the world's writing systems. The originally proposed encodings of the UCS, however, were not compatible with many current applications and protocols, and this has led to the development of UTF-8, the object of this memo. UTF-8 has the characteristic of preserving the full US-ASCII range, providing compatibility with file systems, parsers and other software that rely on US-ASCII values but are transparent to other values. This memo obsoletes and replaces RFC 2279. Internet technical specifications often need to define a formal syntax. Over the years, a modified version of Backus-Naur Form (BNF), called Augmented BNF (ABNF), has been popular among many Internet specifications. The current specification documents ABNF. It balances compactness and simplicity with reasonable representational power. The differences between standard BNF and ABNF involve naming rules, repetition, alternatives, order-independence, and value ranges. This specification also supplies additional rule definitions and encoding for a core lexical analyzer of the type common to several Internet specifications. [STANDARDS-TRACK] JavaScript Object Notation (JSON) is a lightweight, text-based, language-independent data interchange format. It was derived from the ECMAScript Programming Language Standard. JSON defines a small set of formatting rules for the portable representation of structured data. This document removes inconsistencies with other specifications of JSON, repairs specification errors, and offers experience-based interoperability guidance. I-JSON (short for "Internet JSON") is a restricted profile of JSON designed to maximize interoperability and increase confidence that software can process it successfully with predictable results. This document defines procedures for the specification and registration of media types for use in HTTP, MIME, and other Internet protocols. This memo documents an Internet Best Current Practice. Universität Bremen TZI Textuality This document specifies I-Regexp, a flavor of regular expressions that is limited in scope with the goal of interoperation across many different regular-expression libraries. In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. Informative References All RFCs are required to have a Security Considerations section. Historically, such sections have been relatively weak. This document provides guidelines to RFC authors on how to write a good Security Considerations section. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. JSON Pointer defines a string syntax for identifying a specific value within a JavaScript Object Notation (JSON) document. Fachhochschule Dortmund ISO n.d. Ecma International

Inspired by XPath This appendix is informative. At the time JSONPath was invented, XML was noted for the availability of powerful tools to analyse, transform and selectively extract data from XML documents. is one of these tools. In 2007, the need for something solving the same class of problems for the emerging JSON community became apparent, specifically for:

• Finding data interactively and extracting them out of JSON values without special scripting.
• Specifying the relevant parts of the JSON data in a request by a client, so the server can reduce the amount of data in its response, minimizing bandwidth usage.

(Note that XPath has evolved since 2007, and recent versions even nominally support operating inside JSON values. This appendix only discusses the more widely used version of XPath that was available in 2007.) JSONPath picks up the overall feeling of XPath, but maps the concepts to syntax (and partially semantics) that would be familiar to someone using JSON in a dynamic language. E.g., in popular dynamic programming languages such as JavaScript, Python and PHP, the semantics of the XPath expression can be realized in the expression or, in bracket notation, with the variable x holding the argument. The JSONPath language was designed to:

• be naturally based on those language characteristics;
• cover only the most essential parts of XPath 1.0;
• be lightweight in code size and memory consumption;
• be runtime efficient.

JSONPath and XPath JSONPath expressions apply to JSON values in the same way as XPath expressions are used in combination with an XML document. JSONPath uses $ to refer to the root node of the argument, similar to XPath's / at the front. JSONPath expressions move further down the hierarchy using dot notation ($.store.book[0].title) or the bracket notation ($['store']['book'][0]['title']), a lightweight/limited, and a more heavyweight syntax replacing XPath's / within query expressions. Both JSONPath and XPath use * for a wildcard. The descendant operator .., borrowed from , is similar to XPath's //. The array slicing construct [start:end:step] is unique to JSONPath, inspired by from ECMASCRIPT 4. Filter expressions are supported via the syntax ?(<boolean expr>) as in extends by providing a comparison with similar XPath concepts. XPath syntax compared to JSONPath

XPath	JSONPath	Description
/	$	the root XML element
.	@	the current XML element
/	. or []	child operator
..	n/a	parent operator
//	..	nested descendants (JSONPath borrows this syntax from E4X)
*	*	wildcard: All XML elements regardless of their names
@	n/a	attribute access: JSON values do not have attributes
[]	[]	subscript operator used to iterate over XML element collections and for predicates
|	[,]	Union operator (results in a combination of node sets); called list operator in JSONPath, allows combining member names, array indices, and slices
n/a	[start:end:step]	array slice operator borrowed from ES4
[]	?()	applies a filter (script) expression
seamless	n/a	expression engine
()	n/a	grouping

For further illustration, shows some XPath expressions and their JSONPath equivalents. Example XPath expressions and their JSONPath equivalents

XPath	JSONPath	Result
/store/book/author	$.store.book[*].author	the authors of all books in the store
//author	$..author	all authors
/store/*	$.store.*	all things in store, which are some books and a red bicycle
/store//price	$.store..price	the prices of everything in the store
//book[3]	$..book[2]	the third book
//book[last()]	$..book[-1]	the last book in order
//book[position()<3]	$..book[0,1] $..book[:2]	the first two books
//book[isbn]	$..book[?(@.isbn)]	filter all books with isbn number
//book[price<10]	$..book[?(@.price<10)]	filter all books cheaper than 10
//*	$..*	all elements in XML document; all member values and array elements contained in input value

XPath has a lot more functionality (location paths in unabbreviated syntax, operators and functions) than listed in this comparison. Moreover, there are significant differences in how the subscript operator works in XPath and JSONPath:

• Square brackets in XPath expressions always operate on the node set resulting from the previous path fragment. Indices always start at 1.
• With JSONPath, square brackets operate on the object or array addressed by the previous path fragment. Array indices always start at 0.

JSON Pointer This appendix is informative. JSONPath is not intended as a replacement for, but as a more powerful companion to, JSON Pointer . The purposes of the two standards are different. JSON Pointer is for identifying a single value within a JSON document whose structure is known. JSONPath can identify a single value within a JSON document, for example by using a Normalized Path. But JSONPath is also a query syntax that can be used to search for and extract multiple values from JSON documents whose structure is known only in a general way. A Normalized JSONPath can be converted into a JSON Pointer by converting the syntax, without knowledge of any JSON document. The inverse is not generally true: a numeric path component in a JSON Pointer may identify a member of a JSON object or may index an array. For conversion to a JSONPath query, knowledge of the structure of the JSON document is needed to distinguish these cases.

Acknowledgements This specification is based on 's original online article defining JSONPath . The books example was taken from http://coli.lili.uni-bielefeld.de/~andreas/Seminare/sommer02/books.xml -- a dead link now.

Contributors InfluxData, Inc.

Pisa IT mmikulicic@gmail.com

TheSoul Publishing Ltd.

Limassol Cyprus esurov.tsp@gmail.com