Install yamale with Homebrew, apt, Nix

Project links

• Homepage
• Upstream docs
• Package manager page

Commands and aliases

• yamale

Project history

23andMe published the Yamale repository in January 2014. The README describes it simply as a schema and validator for YAML, with both CLI and Python API entry points. Its schema format keeps schemas as YAML documents whose leaves are validator expressions such as `str()`, `int()`, includes, recursion, strict-mode controls, and custom validators.

The PyPI history shows public releases beginning in June 2014 and continued maintenance into the 6.x series. Over time the README added Python 3-only requirements, optional ruamel.yaml parsing for YAML 1.2 support, multiprocessing CLI validation, strict-mode controls, and a warning that schemas should come from trusted sources because the schema language is executable enough to be treated as a trust boundary.

Adoption history

Yamale adoption is mostly practical: teams with YAML configuration, data files, or repository conventions can add a schema file and run a CLI check in tests or continuous integration. It is attractive when a project wants a readable schema next to YAML data without converting the validation problem to JSON Schema.

How it is used

From the command line, Yamale searches a target path for YAML files and looks nearby or upward for a schema file unless one is specified. From Python, callers build schema and data objects with `yamale.make_schema` and `yamale.make_data`, then call `yamale.validate` and handle validation errors.

Yamale is best suited to project-owned schemas: configuration contracts, fixtures, data drops, and repository policy checks. Its own README cautions against accepting malicious schema definitions from untrusted sources.

Why package nerds care

For package nerds, Yamale is a tidy example of a domain-specific validator that stayed deliberately smaller than JSON Schema. It shows up as both a CLI package and a Python import, useful for making YAML-heavy projects less ambiguous without buying into a larger schema ecosystem.

Timeline

• 2014-01: The public GitHub repository was created under 23andMe.
• 2014-06: PyPI records the earliest available Yamale release uploads.
• 2020s: The README documents Python 3.8+, optional ruamel.yaml parsing, CLI multiprocessing, includes, recursion, and strict-mode behavior.
• 2025: PyPI records the 6.x release line.

Related projects

• Yamale sits near JSON Schema validators, PyKwalify, Cerberus-style Python validators, and YAML linters, but it keeps its own compact schema expression syntax rather than adopting JSON Schema as the schema language.

Sources

• https://api.github.com/repos/23andMe/Yamale
• https://github.com/23andMe/Yamale#readme
• https://pypi.org/pypi/yamale/json