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YAML Test Suite

Comprehensive Test Suite for YAML


This repository contains data for testing the correctness of YAML processors.

The types of data include:

  • Metadata about the test
    • Name (short phrase)
    • Tags
    • Description
  • Input YAML
  • Canonical output YAML
  • Matching JSON
  • Token stream notation
  • Event stream notation
  • Error data
  • etc

To get a quick overview of the tests you can have a look at the YAML Test Matrix, made from

You can also view the latest test results from 15 different parsers in this Google sheet.


The tests are available in 2 forms. Files in the src directory encode all the data for YAML using YAML. The data from these tests is also available in a form where each test has its own directory.

For that, use the latest data release under

git clone -b data-YYYY-MM-DD

There are tests which have multiple similar subtests. Those subtests are in their own numeric directories under the parent id, e.g.:


The releases are made from the data branch, which is made from the data in the YAML in the main branch. You shouldn't use the data branch directly as the branch contains unreleased commits which might be wrong, and it is squashed and force pushed from time to time.

Special Characters

The YAML files use a number of non-ascii unicode characters to indicate the presence of certain characters that would be otherwise hard to read.

  • is used for trailing space characters
  • Hard tabs are reresented by one of: (expanding to 4 spaces)
    • ———»
    • ——»
    • —»
    • »
  • us used to show trailing newline characters
  • is used at the end when there is no final newline character
  • indicates a carriage return character
  • indicates a byte order mark (BOM) character

Also these are used in test event output:

  • <SPC> for a space character
  • <TAB> for a tab character

The data branch files

The YAML test files in the src/ dir are turned into data files in the data branch. The make data-update command generates the data branch files under the ./data/ directory. For instance, a file src/AB3D.yaml will generate a data/AB3D/ directory.

A YAML test file can have 1 or more tests. Originally each file had one test, and all the data files were under data/AB3D/. If a YAML test file has more than one test, subdirectories are created: data/AB3D/00/, data/AB3D/01/, data/AB3D/02/, etc.

The test files are:

  • === -- The name/label of the test
  • in.yaml -- The YAML input to be parsed or loaded
  • test.event -- The event DSL produced by the parser test program
  • in.json -- The JSON value that shoiuld load the same as in.yaml
  • out.yaml -- The most normal output a dumper would produce
  • error -- This file indicates the YAML should fail to parse
  • emit.yaml -- Output an emitter would produce

Makefile Targets

The Makefile has a number of targets for automating the process of adding new tests and also preprocessing them into the data branch.

  • make data

    Create a data worktree subdirectory with all the tests as data files.

  • make data-update

    Update the data branch directory with the latest info in the src directory.

  • make export

    Creates an export.tsv file with all the data from the src test files. This tsv data can be copied into a google spreadsheet. The YAML parser playground has a button to copy a test to the same tsv form.

  • make import

    Make a directory called new from a file named import.tsv. The import.tsv file should have data copied from a google spreadsheet.

  • make add-new

    Copy the new tests under new/ into src/ to make a PR for new tests.

  • make testml

    Generate .tml files under a testml/ directory for all the suite tests.

  • make clean

    Remove generated files and directories.

Libaries using this test suite

If your library is using the test suite, drop us a line and we can add it here. It would also be nice if you could add a link back to this test suite.