Can I format YAML without uploading it?

Yes. Parsing and formatting happen locally in the browser.

YAML Formatter

Paste YAML to validate its structure and format it for review. Processing stays local in your browser, with errors kept next to the input so you can fix the exact line.

source7 lines

formatted8 lines

service:
  name: gizmobench
  port: 8080
  debug: "yes"
  tags:
    - b
    - a
retries: 3

Status

Valid

Problems

Documents

Schema

YAML 1.2 core

Indent

Keys

1 comment was counted and not carried over: the formatter re-prints the data it parsed.

Valid: no problems, 1 document, read as YAML 1.2 core.

The data this document resolves to

The data this document resolves to under the YAML 1.2 core schema, printed as JSON.

{
  "service": {
    "name": "gizmobench",
    "port": 8080,
    "debug": "yes",
    "tags": [
      "b",
      "a"
    ]
  },
  "retries": 3
}

Key defined twiceport at 2:1 and 4:1
error at 4:1, first at 2:1
debug: yesYAML 1.2 core
debug is the string "yes"
Anchor expanded past the budgetalias bomb
stopped at 5:8, nothing parsed

The YAML this page reads

The reader here was written for this page rather than taken from a library, so the honest thing is to publish what it handles. The first list is what it reads. The second is what it reports by name instead of guessing at, which is the part a validator usually leaves you to find out.

Read

Block mappings and block sequences, nested to any depth this page reads
Compact sequence items (a mapping that starts on the dash line)
Flow collections: [1, 2] and {a: 1}, including empty and multi-line ones
Plain, single-quoted and double-quoted scalars, with the double-quoted escapes
Block scalars: | and >, with the - and + chomping indicators
Anchors, aliases and a counted expansion budget
Several documents in one file, separated by --- and ...
Comments, counted and kept out of the data
The core schema tags !!str, !!int, !!float, !!bool, !!null, !!map and !!seq
An explicit !!bool accepts the older yes, no, on and off spellings

Reported, not read

Merge keys: << is reported as a warning and left as an ordinary key, not merged
The explicit key form: a line that starts with ? is reported, not read
A quoted scalar spread over several lines: use a block scalar instead
Custom and language tags, including !!binary: reported by name, never resolved
%TAG directives and tag shorthands beyond the core set
Comments in format mode: the formatter re-prints the parsed data, so comments are counted and dropped
Timestamps, sexagesimals and the other YAML 1.1 types: they stay strings, which is what YAML 1.2 core says

Every problem this page can report

All 17 of them, each with the line and the column of what it found. A warning is a note about how something resolved and leaves the document valid; an error does not.

Code	Kind	What it means
tab-indent	error	A tab is used to indent a line. YAML never allows one.
bad-indent	error	A line does not line up with the block it is in.
bad-value	error	A line is not a key and a value, or there is more after the value ends.
duplicate-key	error	The same key appears twice in one mapping. Both lines are named.
unclosed-quote	error	A quoted scalar is not closed on its line.
bad-escape	error	A double-quoted scalar carries an escape YAML does not define.
unclosed-flow	error	A [ or { is never closed.
flow-syntax	error	A flow collection is missing a comma or a closing bracket.
explicit-key	error	The explicit key form, a line starting with ?, is not read here.
undefined-alias	error	An alias names an anchor that was never defined above it.
alias-budget	error	Alias expansion passed the node budget, so nothing was parsed.
unsupported-tag	error	A tag outside the core schema is refused by name and never resolved.
tag-mismatch	error	A core tag does not fit its value, such as !!int on a word.
depth	error	Nesting goes deeper than this page reads.
merge-key	warning	The merge key << is a YAML 1.1 extension and stays an ordinary key here.
directive	warning	A directive line is noted; only %YAML is understood.
stopped	error	The reader stopped early because it could not make progress.

Up to 500,000 characters in one pass, read here in your browser with nothing uploaded and no account. Nothing in the document is ever run or fetched: a tag is a string to the reader, a URL is a string, and alias expansion stops after 10,000 copied nodes. Nesting is read 100 levels deep, and the data panel prints the first 20,000 characters of the result. The mode, the two format options and the draft are kept in this browser alone, drafts up to 100,000 characters, and the Start over control above the tool forgets them.

Accuracy. Read by a YAML 1.2 core-schema parser written for this page, so yes and no are strings, only true and false are booleans, and every problem carries a line and a column. Alias expansion stops at a fixed budget rather than hanging the page, a tag outside the core set is refused by name, and the subset this parser reads is listed under the tool. Your document is read in this browser and nothing it names is ever fetched.

Common questions

Can I format YAML without uploading it?: Yes. Parsing and formatting happen locally in the browser.

Read by a YAML 1.2 core-schema parser written for this page, so yes and no are strings, only true and false are booleans, and every problem carries a line and a column. Alias expansion stops at a fixed budget rather than hanging the page, a tag outside the core set is refused by name, and the subset this parser reads is listed under the tool. Your document is read in this browser and nothing it names is ever fetched.