YAML Flow Sequence Missing Comma – Fix [ ] Lists

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Flow-style YAML sequences use square brackets and commas between items. Adjacent mappings or collections without a comma cannot be parsed as separate list entries.

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YAML flow sequence troubleshooting

How to fix a missing comma in a YAML flow sequence

The sample contains two inline mappings inside square brackets but no comma between them. In flow style, the closing brace of one item must be followed by a separator before the next list item begins. This tool is free to use. No account or payment is required.

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What you can do here

  • YAML 1.2 parser validation
  • Duplicate mapping key detection
  • Preloaded broken YAML example
  • Readable parser feedback
  • .yaml and .yml file import
  • Browser-local processing

Steps

  1. Locate the square-bracket flow sequence reported by the parser.
  2. Identify where one item ends and the next item begins.
  3. Insert the missing comma or rewrite the list in block style, then validate again.

Flow-style YAML uses punctuation as structure

Block sequences use dash markers and indentation, while flow sequences resemble JSON arrays. Inside [ ], commas make item boundaries explicit; whitespace between adjacent collections is not a substitute for a separator.

Block style can be easier for long configuration lists

A compact flow sequence is useful for short values, but nested mappings quickly become difficult to review. Rewriting a complex list with dash markers can make later edits less likely to lose commas or braces.

Missing comma between flow sequence items

A comma separates the two inline mapping items.

Invalid YAML

items: [{name: api} {name: web}]

Corrected YAML

items: [{name: api}, {name: web}]

Common questions

Frequently asked questions

Do YAML lists always need commas?

No. Block sequences use dash markers without commas. Flow sequences inside square brackets use comma separators between items.

Can I replace a flow sequence with a block sequence?

Yes when the consuming YAML semantics permit the same sequence value. Block style is often easier to maintain for nested items.

Why does whitespace not separate two flow mappings?

Flow collection syntax uses punctuation for item boundaries, so a comma is required between adjacent collection values.

Recommended next steps

Missing Comma in YAML Flow MappingSeparate key/value pairs inside YAML curly-brace flow mappings.Multiline Implicit Key in YAMLKeep an implicit flow mapping key and its colon on one line in strict YAML.YAML Validator Online – Check YAML SyntaxPaste any YAML document and inspect parser feedback locally.

Debugging a specific YAML issue? Browse YAML troubleshooting.