{"id":45951,"date":"2021-02-17T23:12:34","date_gmt":"2021-02-18T04:12:34","guid":{"rendered":"https:\/\/www.checkmarx.com\/?p=45951"},"modified":"2025-10-29T13:18:09","modified_gmt":"2025-10-29T11:18:09","slug":"yaml","status":"publish","type":"glossary","link":"https:\/\/checkmarx.com\/glossary\/yaml\/","title":{"rendered":"What Is YAML? Format, Syntax &amp; Security Best Practices"},"content":{"rendered":"<h2 class=\"wp-block-heading article-anchor\" id=\"article-anchor-1\"><strong>Intro<\/strong><\/h2>\n\n\n\n<p>YAML (\u201cYAML Ain\u2019t Markup Language\u201d) is a human\u2011readable data\u2011serialization format used widely for configuration files and data exchange. YAML favors readability via indentation to represent hierarchy and supports mappings (key\u2013value), sequences (lists), and scalars (strings, numbers, booleans).<\/p>\n\n\n\n<h2 class=\"wp-block-heading article-anchor\" id=\"article-anchor-2\">\n<br><strong>Why AppSec cares<\/strong>\n<\/h2>\n\n\n\n<p>YAML powers critical automation and infrastructure &#8211; Kubernetes manifests, Docker Compose, GitHub Actions, Helm charts, Ansible, and AWS CloudFormation &#8211; so securing YAML is essential to resilient CI\/CD and cloud\u2011native pipelines.<\/p>\n\n\n\n<h2 class=\"wp-block-heading article-anchor\" id=\"article-anchor-3\">YAML basics: structure &amp; syntax<\/h2>\n\n\n\n<p><\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>\n<strong>Mapping (object):<\/strong> <code>key: value<\/code>\n<\/li>\n\n\n\n<li>\n<strong>Sequence (list):<\/strong> <code>- item<\/code> (leading dashes)<\/li>\n\n\n\n<li>\n<strong>Scalar:<\/strong> strings, numbers, booleans, nulls<\/li>\n\n\n\n<li>\n<strong>Indentation:<\/strong> spaces only; indentation defines nesting<\/li>\n\n\n\n<li>\n<strong>Multi\u2011document:<\/strong> <code>---<\/code> (start), <code>...<\/code> (optional end)<\/li>\n\n\n\n<li>\n<strong>Anchors &amp; aliases:<\/strong> reuse blocks with <code>&amp;name<\/code> and <code>*name<\/code>\n<\/li>\n<\/ul>\n\n\n<div class=\"wp-block-image\">\n<figure class=\"aligncenter size-full is-resized\"><img decoding=\"async\" width=\"788\" height=\"1006\" src=\"https:\/\/checkmarx.com\/wp-content\/uploads\/2021\/02\/YAML-simple-service-definition.png\" alt=\"YAML simple service definition code\" class=\"wp-image-104833\" style=\"width:auto;height:480px\" srcset=\"https:\/\/checkmarx.com\/wp-content\/uploads\/2021\/02\/YAML-simple-service-definition.png 788w, https:\/\/checkmarx.com\/wp-content\/uploads\/2021\/02\/YAML-simple-service-definition-235x300.png 235w, https:\/\/checkmarx.com\/wp-content\/uploads\/2021\/02\/YAML-simple-service-definition-768x980.png 768w\" sizes=\"(max-width: 788px) 100vw, 788px\" \/><\/figure>\n<\/div>\n\n\n<h3 class=\"wp-block-heading\">\n<br>YAML Syntax Example<\/h3>\n\n\n\n<pre class=\"wp-block-code\"><code># A simple service definition\nservice: &amp;svc\n  name: payments\n  port: 8080\n  env:\n    - key: LOG_LEVEL\n      value: \"info\"\n    - key: FEATURE_X\n      value: \"enabled\"\n\ndeployments:\n  - &lt;&lt;: *svc\n    name: payments-staging\n    port: 8081\n  - &lt;&lt;: *svc\n    name: payments-prod\n    port: 80\n<\/code><\/pre>\n\n\n\n<div style=\"height:43px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<p><em>Tip:<\/em> Quote strings like \u201con\u201d, \u201coff\u201d, \u201cyes\u201d, \u201cno\u201d when you intend them as strings &#8211; unquoted they may be parsed as booleans.<\/p>\n\n\n\n<h2 class=\"wp-block-heading article-anchor\" id=\"article-anchor-4\">Where you\u2019ll see YAML in modern stacks<\/h2>\n\n\n\n<ul class=\"wp-block-list\">\n<li>\n<strong>Kubernetes<\/strong> manifests for Pods, Deployments, RBAC, etc.<\/li>\n\n\n\n<li>\n<strong>Docker Compose<\/strong> service definitions (<code>docker-compose.yml<\/code>).<\/li>\n\n\n\n<li>\n<strong>GitHub Actions<\/strong> workflows (<code>.github\/workflows\/*.yml<\/code>).<\/li>\n\n\n\n<li>\n<strong>Helm<\/strong> charts (Kubernetes packaging).<\/li>\n\n\n\n<li>\n<strong>Ansible<\/strong> playbooks and inventories.<\/li>\n\n\n\n<li>\n<strong>AWS CloudFormation<\/strong> templates.<\/li>\n<\/ul>\n\n\n\n<p><strong>Scan YAML as code:<\/strong> Bring YAML into your AppSec program with <strong><a href=\"https:\/\/checkmarx.com\/product\/iac-security\/\">IaC Security<\/a><\/strong>, <strong><a href=\"https:\/\/checkmarx.com\/product\/kics\/\">KICS (open\u2011source)<\/a><\/strong>, and <strong><a href=\"https:\/\/checkmarx.com\/product\/container-security\/\">Container Security<\/a><\/strong> so misconfigurations never make it to production.<\/p>\n\n\n\n<h2 class=\"wp-block-heading article-anchor\" id=\"article-anchor-5\">YAML security risks &amp; best practices<\/h2>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>Common risks<\/strong><\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li>\n<strong>Unsafe deserialization:<\/strong> parsing untrusted YAML using unsafe loaders can enable code execution or DoS in some libraries.<\/li>\n\n\n\n<li>\n<strong>Secrets in plain text:<\/strong> credentials, tokens, or keys embedded in YAML or git history.<\/li>\n\n\n\n<li>\n<strong>Misconfigurations:<\/strong> overly permissive RBAC, insecure defaults, missing validations.<\/li>\n\n\n\n<li>\n<strong>Injection\/overrides:<\/strong> unintended variable substitution or anchor\/alias misuse.<\/li>\n<\/ul>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>How to secure YAML in CI\/CD<\/strong><\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li>\n<strong>Use safe parsers:<\/strong> prefer \u201csafe\u201d constructors\/loaders for untrusted content.<\/li>\n\n\n\n<li>\n<strong>Keep secrets out of YAML:<\/strong> store in a secret manager; add pre\u2011commit &amp; pipeline checks with <strong><a href=\"https:\/\/checkmarx.com\/product\/secrets-detection\/\">Secrets Detection<\/a><\/strong>.<\/li>\n\n\n\n<li>\n<strong>Lint &amp; validate:<\/strong> enforce schemas\/policies (e.g., Kubernetes) in CI.<\/li>\n\n\n\n<li>\n<strong>Scan as part of DevSecOps:<\/strong> add <strong><a href=\"https:\/\/checkmarx.com\/product\/iac-security\/\">IaC Security<\/a><\/strong> or <strong><a href=\"https:\/\/checkmarx.com\/product\/kics\/\">KICS<\/a><\/strong>; correlate with <strong><a href=\"https:\/\/checkmarx.com\/cxsca-open-source-scanning\/\">SCA<\/a><\/strong> and <strong><a href=\"https:\/\/checkmarx.com\/cxsast-source-code-scanning\/\">SAST<\/a><\/strong>.<\/li>\n\n\n\n<li>\n<strong>Least privilege:<\/strong> lock down actions, runners, service accounts, cluster roles.<\/li>\n\n\n\n<li>\n<strong>Repository hygiene:<\/strong> enforce branch protections and monitor with <strong><a href=\"https:\/\/checkmarx.com\/product\/repository-health\/\">Repository Health<\/a><\/strong>.<\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading article-anchor\" id=\"article-anchor-6\">YAML vs. JSON Comparison Table<br>\n<\/h2>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\">\n<thead><tr>\n<th>Aspect<\/th>\n<th>YAML<\/th>\n<th>JSON<\/th>\n<\/tr><\/thead>\n<tbody>\n<tr>\n<td>Readability<\/td>\n<td>Human\u2011friendly; supports comments<\/td>\n<td>Concise; no comments by spec<\/td>\n<\/tr>\n<tr>\n<td>Structure<\/td>\n<td>Indentation defines hierarchy<\/td>\n<td>Braces\/brackets define hierarchy<\/td>\n<\/tr>\n<tr>\n<td>Tooling<\/td>\n<td>Great for configs &amp; templating<\/td>\n<td>Ubiquitous for APIs &amp; services<\/td>\n<\/tr>\n<tr>\n<td>Interoperability<\/td>\n<td>Can embed JSON<\/td>\n<td>Strict grammar; widely supported<\/td>\n<\/tr>\n<tr>\n<td>Security<\/td>\n<td>Beware unsafe loaders; lint &amp; scan<\/td>\n<td>Simpler parser surface<\/td>\n<\/tr>\n<\/tbody>\n<\/table><\/figure>\n\n\n\n<div style=\"height:17px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<section class=\"section-accordion\">\n    <div class=\"main-wrapper section-accordion__wrapper\">\n        <h2 class=\"section-title article-anchor\" id=\"article-anchor-7\">FAQ<\/h2>\n        <div class=\"fag-accordion__wrapper\">\n            <div class=\"js-accordion fag-accordion\">\n                <div>\n\n                                            <div class=\"js-accordion__item fag-accordion__item \">\n                            <h3 class=\"js-accordion__btn fag-accordion__btn\">\n                                <svg width=\"34px\" height=\"23px\" viewbox=\"0 0 34 23\" version=\"1.1\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\">\n                                    <g id=\"Page-1\" stroke=\"none\" stroke-width=\"1\" fill=\"none\" fill-rule=\"evenodd\">\n                                        <g id=\"Shape\" transform=\"translate(0.939453, 1.530000)\" stroke-width=\"3\">\n                                            <path d=\"M19.810947,20.4179 L31.029947,9.14 M30.029947,10.1989 L0,10.1989 M31.029947,11.26 L19.810947,0\"><\/path>\n                                        <\/g>\n                                    <\/g>\n                                <\/svg>\n                                Is a YAML file the same as a YML file?                            <\/h3>\n                            <div class=\"js-accordion-content fag-accordion__content\">\n                                <p data-start=\"19755\" data-end=\"19851\">Yes. <code data-start=\"19805\" data-end=\"19812\">.yaml<\/code> and <code data-start=\"19817\" data-end=\"19823\">.yml<\/code> are both common extensions.<\/p>\n<p data-start=\"19853\" data-end=\"20322\">\n                            <\/p>\n<\/div>\n                        <\/div>\n                                                <div class=\"js-accordion__item fag-accordion__item \">\n                            <h3 class=\"js-accordion__btn fag-accordion__btn\">\n                                <svg width=\"34px\" height=\"23px\" viewbox=\"0 0 34 23\" version=\"1.1\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\">\n                                    <g id=\"Page-1\" stroke=\"none\" stroke-width=\"1\" fill=\"none\" fill-rule=\"evenodd\">\n                                        <g id=\"Shape\" transform=\"translate(0.939453, 1.530000)\" stroke-width=\"3\">\n                                            <path d=\"M19.810947,20.4179 L31.029947,9.14 M30.029947,10.1989 L0,10.1989 M31.029947,11.26 L19.810947,0\"><\/path>\n                                        <\/g>\n                                    <\/g>\n                                <\/svg>\n                                Where should I start to secure YAML at scale?                            <\/h3>\n                            <div class=\"js-accordion-content fag-accordion__content\">\n                                <p>Enforce linting and schema validation in CI, scan with <strong data-start=\"19960\" data-end=\"20023\"><a class=\"decorated-link\" href=\"https:\/\/checkmarx.com\/product\/iac-security\/?utm_source=chatgpt.com\" target=\"_new\" rel=\"noopener\" data-start=\"19962\" data-end=\"20021\">IaC Security<\/a><\/strong> or <strong data-start=\"20027\" data-end=\"20074\"><a class=\"decorated-link\" href=\"https:\/\/checkmarx.com\/product\/kics\/\" target=\"_new\" rel=\"noopener\" data-start=\"20029\" data-end=\"20072\">KICS<\/a><\/strong>, catch secrets with <strong data-start=\"20095\" data-end=\"20168\"><a class=\"decorated-link\" href=\"https:\/\/checkmarx.com\/product\/secrets-detection\/\" target=\"_new\" rel=\"noopener\" data-start=\"20097\" data-end=\"20166\">Secrets Detection<\/a><\/strong>, and correlate risk with <strong data-start=\"20194\" data-end=\"20254\"><a class=\"decorated-link\" href=\"https:\/\/checkmarx.com\/cxsca-open-source-scanning\/\" target=\"_new\" rel=\"noopener\" data-start=\"20196\" data-end=\"20252\">SCA<\/a><\/strong> and <strong data-start=\"20259\" data-end=\"20321\"><a class=\"decorated-link\" href=\"https:\/\/checkmarx.com\/cxsast-source-code-scanning\/\" target=\"_new\" rel=\"noopener\" data-start=\"20261\" data-end=\"20319\">SAST<\/a><\/strong>.<\/p>\n                            <\/div>\n                        <\/div>\n                        <\/div>\n<div>                        <div class=\"js-accordion__item fag-accordion__item \">\n                            <h3 class=\"js-accordion__btn fag-accordion__btn\">\n                                <svg width=\"34px\" height=\"23px\" viewbox=\"0 0 34 23\" version=\"1.1\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\">\n                                    <g id=\"Page-1\" stroke=\"none\" stroke-width=\"1\" fill=\"none\" fill-rule=\"evenodd\">\n                                        <g id=\"Shape\" transform=\"translate(0.939453, 1.530000)\" stroke-width=\"3\">\n                                            <path d=\"M19.810947,20.4179 L31.029947,9.14 M30.029947,10.1989 L0,10.1989 M31.029947,11.26 L19.810947,0\"><\/path>\n                                        <\/g>\n                                    <\/g>\n                                <\/svg>\n                                Does YAML replace JSON?                            <\/h3>\n                            <div class=\"js-accordion-content fag-accordion__content\">\n                                <p data-start=\"20324\" data-end=\"20412\">No &#8211; choose the format that fits your tooling and workflows.<\/p>\n<p data-start=\"20414\" data-end=\"20558\">\n                            <\/p>\n<\/div>\n                        <\/div>\n                                                <div class=\"js-accordion__item fag-accordion__item \">\n                            <h3 class=\"js-accordion__btn fag-accordion__btn\">\n                                <svg width=\"34px\" height=\"23px\" viewbox=\"0 0 34 23\" version=\"1.1\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\">\n                                    <g id=\"Page-1\" stroke=\"none\" stroke-width=\"1\" fill=\"none\" fill-rule=\"evenodd\">\n                                        <g id=\"Shape\" transform=\"translate(0.939453, 1.530000)\" stroke-width=\"3\">\n                                            <path d=\"M19.810947,20.4179 L31.029947,9.14 M30.029947,10.1989 L0,10.1989 M31.029947,11.26 L19.810947,0\"><\/path>\n                                        <\/g>\n                                    <\/g>\n                                <\/svg>\n                                What are some YAML \u201cgotchas\u201d?                            <\/h3>\n                            <div class=\"js-accordion-content fag-accordion__content\">\n                                <p data-start=\"20414\" data-end=\"20558\">Spaces (not tabs), accidental booleans (<code data-start=\"20490\" data-end=\"20505\">on\/off\/yes\/no<\/code>), and anchors\/aliases misuse. Add linters and tests.<\/p>\n                            <\/div>\n                        <\/div>\n                                        <\/div>\n            <\/div>\n        <\/div>\n    <\/div>\n<\/section>\n\n\n<script type=\"application\/ld+json\">{\"@context\":\"https:\/\/schema.org\",\"@type\":\"FAQPage\",\"url\":\"https:\/\/checkmarx.com\/glossary\/yaml\/\",\"mainEntity\":[{\"@type\":\"Question\",\"name\":\"Is a YAML file the same as a YML file?\",\"acceptedAnswer\":{\"@type\":\"Answer\",\"text\":\"Yes. .yaml and .yml are both common extensions.\"}},{\"@type\":\"Question\",\"name\":\"Where should I start to secure YAML at scale?\",\"acceptedAnswer\":{\"@type\":\"Answer\",\"text\":\"Enforce linting and schema validation in CI, scan with IaC Security or KICS, catch secrets with Secrets Detection, and correlate risk with SCA and SAST.\"}},{\"@type\":\"Question\",\"name\":\"Does YAML replace JSON?\",\"acceptedAnswer\":{\"@type\":\"Answer\",\"text\":\"No &#8211; choose the format that fits your tooling and workflows.\"}},{\"@type\":\"Question\",\"name\":\"What are some YAML \u201cgotchas\u201d?\",\"acceptedAnswer\":{\"@type\":\"Answer\",\"text\":\"Spaces (not tabs), accidental booleans (on\/off\/yes\/no), and anchors\/aliases misuse. Add linters and tests.\"}}]}<\/script>","protected":false},"excerpt":{"rendered":"<p>Intro YAML (\u201cYAML Ain\u2019t Markup Language\u201d) is a human\u2011readable data\u2011serialization format used widely for configuration files and data exchange. YAML favors readability via indentation to represent hierarchy and supports mappings (key\u2013value), sequences (lists), and scalars (strings, numbers, booleans). Why AppSec cares YAML powers critical automation and infrastructure &#8211; Kubernetes manifests, Docker Compose, GitHub Actions, Helm [&hellip;]<\/p>\n","protected":false},"author":11,"featured_media":103122,"template":"","glossary-tags":[866,1437],"class_list":["post-45951","glossary","type-glossary","status-publish","has-post-thumbnail","hentry","glossary-tags-container-security","glossary-tags-languages"],"acf":[],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v27.1.1 - https:\/\/yoast.com\/product\/yoast-seo-wordpress\/ -->\n<title>What Is YAML? 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