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Query JSON with JMESPath#

JMESPath is a query language for JSON, allowing you to extract and transform elements from a JSON document. For full details of how to use JMESPath, refer to the JMESPath documentation.

The $jmespath() method#

n8n provides a custom method, $jmespath(). It allows you to perform a search on a JSON object using the JMESPath query language.

The basic syntax is: 

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$jmespath(object, searchString)

To help understand what the method does, here is the equivalent longer JavaScript:

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var jmespath = require('jmespath');
jmespath.search(object, searchString);

object is a JSON object, such as the output of a previous node. searchString is an expression written in the JMESPath query language. The JMESPath Specification provides a list of supported expressions, while their Tutorial and Examples provide interactive examples.

Search parameter order

The examples in the JMESPath Specification follow the pattern search(searchString, object). The JMESPath JavaScript library, which n8n uses, supports search(object, searchString) instead. This means that when using examples from the JMESPath documentation, you may need to change the order of the search function parameters.

Common tasks#

This section provides examples for some common operations. More examples, and detailed guidance, are available in JMESPath's own documentation.

A shorter way to write basic operations#

JMESPath provides a shorter and more readable way to write basic JSON queries.

Consider the following scenario: you have a webhook trigger that receives data through the webhook body. You want to extract some of that data for use in the workflow.

Your webhook data looks similar to this:

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[
  {
    "headers": {
      "host": "n8n.instance.address",
      ...
    },
    "params": {},
    "query": {},
    "body": {
      "name": "Jim",
      "age": 30,
      "city": "New York",
      "dogs": ["Fido", "Spot"]
    }
  }
]

Extract the city:

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// With JMESPath
$json.body.city
// Without JMESPath
$json['body']['city']

Get the first dog in dogs[]:

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// With JMESPath
$json.body.dogs[0]
// Without JMESPath
$json['body']['dogs'][0]

Apply a JMESPath expression to a collection of elements with projections#

From the JMESPath projections documentation:

Projections are one of the key features of JMESPath. It allows you to apply an expression to a collection of elements. JMESPath supports five kinds of projections:

  • List Projections
  • Slice Projections
  • Object Projections
  • Flatten Projections
  • Filter Projections

The following example shows basic usage of list, slice, and object projections. Refer to the JMESPath projections documentation for detailed explanations of each projection type, and more examples.

Given this JSON from a webhook node:

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[
  {
    "headers": {
      "host": "n8n.instance.address",
      ...
    },
    "params": {},
    "query": {},
    "body": {
      "people": [
        {
          "first": "James",
          "last": "Green"
        },
        {
          "first": "Jacob",
          "last": "Jones"
        },
        {
          "first": "Jayden",
          "last": "Smith"
        }
      ],
      "dogs": {
        "Fido": {
          "color": "brown",
          "age": 7
        },
        "Spot": {
          "color": "black and white",
          "age": 5
        }
      }
    }
  }
]

Retrieve a list of all the people's first names:

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$jmespath($json.body.people, "[*].first" )
/* Returns:
[
  {
    "firstNames": [
      "James",
      "Jacob",
      "Jayden"
    ]
  }
]
*/

Get a slice of the first names:

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$jmespath($json.body.people, "[:2].first")
/* Returns:
[
  {
    "firstNames": [
      "James",
      "Jacob",
      "Jayden"
    ]
  }
]
*/

Get a list of the dogs' ages using object projections:

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$jmespath($json.body.dogs, "*.age")
/* Returns:
[
    7,
    5
]
*/

Select multiple elements and create a new list or object#

Multiselect allows you to select elements from a JSON object and combine them into a new list or object.

Given this JSON from a webhook node:

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[
  {
    "headers": {
      "host": "n8n.instance.address",
      ...
    },
    "params": {},
    "query": {},
    "body": {
      "people": [
        {
          "first": "James",
          "last": "Green"
        },
        {
          "first": "Jacob",
          "last": "Jones"
        },
        {
          "first": "Jayden",
          "last": "Smith"
        }
      ],
      "dogs": {
        "Fido": {
          "color": "brown",
          "age": 7
        },
        "Spot": {
          "color": "black and white",
          "age": 5
        }
      }
    }
  }
]

Use multiselect list to get the first and last names and create new lists containing both names:

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$jmespath($json.body.people, "[].[first, last]")
/* Returns:
[
  {
    "fullNames": [
      [
        "James",
        "Green"
      ],
      [
        "Jacob",
        "Jones"
      ],
      [
        "Jayden",
        "Smith"
      ]
    ]
  }
]
*/