gh-czlonkowski-n8n-skills/skills/n8n-expression-syntax/COMMON_MISTAKES.md

Common n8n Expression Mistakes

Complete catalog of expression errors with explanations and fixes.

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1. Missing Curly Braces

Problem: Expression not recognized, shows as literal text

❌ Wrong:

$json.email

✅ Correct:

{{$json.email}}

Why it fails: n8n treats text without {{ }} as a literal string. Expressions must be wrapped to be evaluated.

How to identify: Field shows exact text like "$json.email" instead of actual value.

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2. Webhook Body Access

Problem: Undefined values when accessing webhook data

❌ Wrong:

{{$json.name}}
{{$json.email}}
{{$json.message}}

✅ Correct:

{{$json.body.name}}
{{$json.body.email}}
{{$json.body.message}}

Why it fails: Webhook node wraps incoming data under .body property. The root $json contains headers, params, query, and body.

Webhook structure:

{
  "headers": {...},
  "params": {...},
  "query": {...},
  "body": {         // User data is HERE!
    "name": "John",
    "email": "john@example.com"
  }
}

How to identify: Webhook workflow shows "undefined" for fields that are definitely being sent.

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3. Spaces in Field Names

Problem: Syntax error or undefined value

❌ Wrong:

{{$json.first name}}
{{$json.user data.email}}

✅ Correct:

{{$json['first name']}}
{{$json['user data'].email}}

Why it fails: Spaces break dot notation. JavaScript interprets space as end of property name.

How to identify: Error message about unexpected token, or undefined when field exists.

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4. Spaces in Node Names

Problem: Cannot access other node's data

❌ Wrong:

{{$node.HTTP Request.json.data}}
{{$node.Respond to Webhook.json}}

✅ Correct:

{{$node["HTTP Request"].json.data}}
{{$node["Respond to Webhook"].json}}

Why it fails: Node names are treated as object property names and need quotes when they contain spaces.

How to identify: Error like "Cannot read property 'Request' of undefined"

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5. Incorrect Node Reference Case

Problem: Undefined or wrong data returned

❌ Wrong:

{{$node["http request"].json.data}}  // lowercase
{{$node["Http Request"].json.data}}  // wrong capitalization

✅ Correct:

{{$node["HTTP Request"].json.data}}  // exact match

Why it fails: Node names are case-sensitive. Must match exactly as shown in workflow.

How to identify: Undefined value even though node exists and has data.

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6. Double Wrapping

Problem: Literal {{ }} appears in output

❌ Wrong:

{{{$json.field}}}

✅ Correct:

{{$json.field}}

Why it fails: Only one set of {{ }} is needed. Extra braces are treated as literal characters.

How to identify: Output shows "{{value}}" instead of just "value".

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7. Array Access with Dots

Problem: Syntax error or undefined

❌ Wrong:

{{$json.items.0.name}}
{{$json.users.1.email}}

✅ Correct:

{{$json.items[0].name}}
{{$json.users[1].email}}

Why it fails: Array indices require brackets, not dots. Number after dot is invalid JavaScript.

How to identify: Syntax error or "Cannot read property '0' of undefined"

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8. Using Expressions in Code Nodes

Problem: Literal string instead of value, or errors

❌ Wrong (in Code node):

const email = '{{$json.email}}';
const name = '={{$json.body.name}}';

✅ Correct (in Code node):

const email = $json.email;
const name = $json.body.name;

// Or using Code node API
const email = $input.item.json.email;
const allItems = $input.all();

Why it fails: Code nodes have direct access to data. The {{ }} syntax is for expression fields in other nodes, not for JavaScript code.

How to identify: Literal string "{{$json.email}}" appears in Code node output instead of actual value.

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9. Missing Quotes in $node Reference

Problem: Syntax error

❌ Wrong:

{{$node[HTTP Request].json.data}}

✅ Correct:

{{$node["HTTP Request"].json.data}}

Why it fails: Node names must be quoted strings inside brackets.

How to identify: Syntax error "Unexpected identifier"

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10. Incorrect Property Path

Problem: Undefined value

❌ Wrong:

{{$json.data.items.name}}       // items is an array
{{$json.user.email}}            // user doesn't exist, it's userData

✅ Correct:

{{$json.data.items[0].name}}    // access array element
{{$json.userData.email}}        // correct property name

Why it fails: Wrong path to data. Arrays need index, property names must be exact.

How to identify: Check actual data structure using expression editor preview.

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11. Using = Prefix Outside JSON

Problem: Literal "=" appears in output

❌ Wrong (in text field):

Email: ={{$json.email}}

✅ Correct (in text field):

Email: {{$json.email}}

Note: The = prefix is only needed in JSON mode or when you want to set entire field value to expression result:

// JSON mode (set property to expression)
{
  "email": "={{$json.body.email}}"
}

// Text mode (no = needed)
Hello {{$json.body.name}}!

Why it fails: The = is parsed as literal text in non-JSON contexts.

How to identify: Output shows "=john@example.com" instead of "john@example.com"

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12. Expressions in Webhook Path

Problem: Path doesn't update, validation error

❌ Wrong:

path: "{{$json.user_id}}/webhook"
path: "users/={{$env.TENANT_ID}}"

✅ Correct:

path: "my-webhook"              // Static paths only
path: "user-webhook/:userId"    // Use dynamic URL parameters instead

Why it fails: Webhook paths must be static. Use dynamic URL parameters (:paramName) instead of expressions.

How to identify: Webhook path doesn't change or validation warns about invalid path.

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13. Forgetting .json in $node Reference

Problem: Undefined or wrong data

❌ Wrong:

{{$node["HTTP Request"].data}}          // Missing .json
{{$node["Webhook"].body.email}}         // Missing .json

✅ Correct:

{{$node["HTTP Request"].json.data}}
{{$node["Webhook"].json.body.email}}

Why it fails: Node data is always under .json property (or .binary for binary data).

How to identify: Undefined value when you know the node has data.

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14. String Concatenation Confusion

Problem: Attempting JavaScript template literals

❌ Wrong:

`Hello ${$json.name}!`          // Template literal syntax
"Hello " + $json.name + "!"     // String concatenation

✅ Correct:

Hello {{$json.name}}!           // n8n expressions auto-concatenate

Why it fails: n8n expressions don't use JavaScript template literal syntax. Adjacent text and expressions are automatically concatenated.

How to identify: Literal backticks or + symbols appear in output.

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15. Empty Expression Brackets

Problem: Literal {{}} in output

❌ Wrong:

{{}}
{{ }}

✅ Correct:

{{$json.field}}                 // Include expression content

Why it fails: Empty expression brackets have nothing to evaluate.

How to identify: Literal "{{ }}" text appears in output.

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Quick Reference Table

Error	Symptom	Fix
No {{ }}	Literal text	Add {{ }}
Webhook data	Undefined	Add .body
Space in field	Syntax error	Use ['field name']
Space in node	Undefined	Use ["Node Name"]
Wrong case	Undefined	Match exact case
Double {{ }}	Literal braces	Remove extra {{ }}
.0 array	Syntax error	Use [0]
{{ }} in Code	Literal string	Remove {{ }}
No quotes in $node	Syntax error	Add quotes
Wrong path	Undefined	Check data structure
= in text	Literal =	Remove = prefix
Dynamic path	Doesn't work	Use static path
Missing .json	Undefined	Add .json
Template literals	Literal text	Use {{ }}
Empty {{ }}	Literal braces	Add expression

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Debugging Process

When expression doesn't work:

1. Check braces: Is it wrapped in {{ }}?
2. Check data source: Is it webhook data? Add .body
3. Check spaces: Field or node name has spaces? Use brackets
4. Check case: Does node name match exactly?
5. Check path: Is the property path correct?
6. Use expression editor: Preview shows actual result
7. Check context: Is it a Code node? Remove {{ }}

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Related: See EXAMPLES.md for working examples of correct syntax.