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content="kdl is a document language, mostly based on SDLang, with xml-like semantics that looks like you're invoking a bunch of CLI commands!"
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<title>The KDL Document Language</title>
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<main><header class="pt-20 pb-10 px-4">
<img src="./logo-with-tagline.svg" class="mx-auto h-40" alt="KDL: A cuddly document language">
</header>
<section class="kdl-section" id="description">
<p>KDL is a small, pleasing document language with xml-like semantics that looks
like you're invoking a bunch of CLI commands! It's meant to be used both as a
serialization format and a configuration language, much like JSON, YAML, or
XML. It looks like this:</p>
<pre class="shiki" style="background-color: #2e3440ff"><code><span class="line"><span style="color: #81A1C1">package</span><span style="color: #D8DEE9FF"> {</span></span>
<span class="line"><span style="color: #D8DEE9FF"> </span><span style="color: #81A1C1">name</span><span style="color: #D8DEE9FF"> </span><span style="color: #A3BE8C">&quot;my-pkg&quot;</span></span>
<span class="line"><span style="color: #D8DEE9FF"> </span><span style="color: #81A1C1">version</span><span style="color: #D8DEE9FF"> </span><span style="color: #A3BE8C">&quot;1.2.3&quot;</span></span>
<span class="line"><span style="color: #D8DEE9FF"> </span><span style="color: #81A1C1">dependencies</span><span style="color: #D8DEE9FF"> {</span></span>
<span class="line"><span style="color: #D8DEE9FF"> </span><span style="color: #616E88">// Nodes can have standalone values as well as key/value pairs.</span></span>
<span class="line"><span style="color: #D8DEE9FF"> </span><span style="color: #81A1C1">lodash</span><span style="color: #D8DEE9FF"> </span><span style="color: #A3BE8C">&quot;^3.2.1&quot;</span><span style="color: #D8DEE9FF"> </span><span style="color: #8FBCBB">optional</span><span style="color: #ECEFF4">=</span><span style="color: #81A1C1">true</span><span style="color: #D8DEE9FF"> </span><span style="color: #8FBCBB">alias</span><span style="color: #ECEFF4">=</span><span style="color: #A3BE8C">&quot;underscore&quot;</span></span>
<span class="line"><span style="color: #D8DEE9FF"> }</span></span>
<span class="line"><span style="color: #D8DEE9FF"> </span><span style="color: #81A1C1">scripts</span><span style="color: #D8DEE9FF"> {</span></span>
<span class="line"><span style="color: #D8DEE9FF"> </span><span style="color: #616E88">// &quot;Raw&quot; and multi-line strings are supported.</span></span>
<span class="line"><span style="color: #D8DEE9FF"> </span><span style="color: #81A1C1">build</span><span style="color: #D8DEE9FF"> </span><span style="color: #A3BE8C">r#&quot;</span></span>
<span class="line"><span style="color: #A3BE8C"> echo &quot;foo&quot;</span></span>
<span class="line"><span style="color: #A3BE8C"> node -c &quot;console.log(&#39;hello, world!&#39;);&quot;</span></span>
<span class="line"><span style="color: #A3BE8C"> echo &quot;foo&quot; &gt; some-file.txt</span></span>
<span class="line"><span style="color: #A3BE8C"> &quot;#</span></span>
<span class="line"><span style="color: #D8DEE9FF"> }</span></span>
<span class="line"><span style="color: #D8DEE9FF"> </span><span style="color: #616E88">// `\` breaks up a single node across multiple lines.</span></span>
<span class="line"><span style="color: #D8DEE9FF"> </span><span style="color: #81A1C1">the-matrix</span><span style="color: #D8DEE9FF"> </span><span style="color: #B48EAD">1</span><span style="color: #D8DEE9FF"> </span><span style="color: #B48EAD">2</span><span style="color: #D8DEE9FF"> </span><span style="color: #B48EAD">3</span><span style="color: #D8DEE9FF"> \</span></span>
<span class="line"><span style="color: #D8DEE9FF"> </span><span style="color: #B48EAD">4</span><span style="color: #D8DEE9FF"> </span><span style="color: #B48EAD">5</span><span style="color: #D8DEE9FF"> </span><span style="color: #B48EAD">6</span><span style="color: #D8DEE9FF"> \</span></span>
<span class="line"><span style="color: #D8DEE9FF"> </span><span style="color: #B48EAD">7</span><span style="color: #D8DEE9FF"> </span><span style="color: #B48EAD">8</span><span style="color: #D8DEE9FF"> </span><span style="color: #B48EAD">9</span></span>
<span class="line"><span style="color: #D8DEE9FF"> </span><span style="color: #616E88">// &quot;Slashdash&quot; comments operate at the node level, with just `/-`.</span></span>
<span class="line"><span style="color: #D8DEE9FF"> </span><span style="color: #616E88">/-this-is-commented </span><span style="color: #D8DEE9FF">{</span></span>
<span class="line"><span style="color: #D8DEE9FF"> </span><span style="color: #81A1C1">this</span><span style="color: #D8DEE9FF"> </span><span style="color: #A3BE8C">&quot;entire&quot;</span><span style="color: #D8DEE9FF"> </span><span style="color: #A3BE8C">&quot;node&quot;</span><span style="color: #D8DEE9FF"> {</span></span>
<span class="line"><span style="color: #D8DEE9FF"> </span><span style="color: #A3BE8C">&quot;is&quot;</span><span style="color: #D8DEE9FF"> </span><span style="color: #A3BE8C">&quot;gone&quot;</span></span>
<span class="line"><span style="color: #D8DEE9FF"> }</span></span>
<span class="line"><span style="color: #D8DEE9FF"> }</span></span>
<span class="line"><span style="color: #D8DEE9FF">}</span></span></code></pre>
<p>There's a living <a href="https://github.com/kdl-org/kdl/blob/main/SPEC.md">specification</a>, as well as various
<a href="#implementations">implementations</a>. You can also check out the <a href="#faq">FAQ</a> to
answer all your burning questions!</p>
<p>In addition to a spec for KDL itself, there are also standard specs for <a href="https://github.com/kdl-org/kdl/blob/main/QUERY-SPEC.md">a KDL
Query Language</a> based
on CSS selectors, and <a href="https://github.com/kdl-org/kdl/blob/main/SCHEMA-SPEC.md">a KDL Schema
Language</a> loosely
based on JSON Schema.</p>
<p>The language is based on <a href="https://sdlang.org">SDLang</a>, with a number of
modifications and clarifications on its syntax and behavior.</p>
<p>The current version of the KDL spec is <code>1.0.0</code>.</p>
<p><a href="https://kdl-play.danini.dev/">Play with it in your browser!</a></p>
</section>
<section class="kdl-section" id="overview">
<h2>Overview</h2>
<h3>Basics</h3>
<p>A KDL node is a node name, followed by zero or more &quot;arguments&quot;, and
children.</p>
<pre class="shiki" style="background-color: #2e3440ff"><code><span class="line"><span style="color: #81A1C1">title</span><span style="color: #D8DEE9FF"> </span><span style="color: #A3BE8C">&quot;Hello, World&quot;</span></span></code></pre>
<p>You can also have multiple values in a single node!</p>
<pre class="shiki" style="background-color: #2e3440ff"><code><span class="line"><span style="color: #81A1C1">bookmarks</span><span style="color: #D8DEE9FF"> </span><span style="color: #B48EAD">12</span><span style="color: #D8DEE9FF"> </span><span style="color: #B48EAD">15</span><span style="color: #D8DEE9FF"> </span><span style="color: #B48EAD">188</span><span style="color: #D8DEE9FF"> </span><span style="color: #B48EAD">1234</span></span></code></pre>
<p>Nodes can have properties.</p>
<pre class="shiki" style="background-color: #2e3440ff"><code><span class="line"><span style="color: #81A1C1">author</span><span style="color: #D8DEE9FF"> </span><span style="color: #A3BE8C">&quot;Alex Monad&quot;</span><span style="color: #D8DEE9FF"> </span><span style="color: #8FBCBB">email</span><span style="color: #ECEFF4">=</span><span style="color: #A3BE8C">&quot;alex@example.com&quot;</span><span style="color: #D8DEE9FF"> </span><span style="color: #8FBCBB">active</span><span style="color: #ECEFF4">=</span><span style="color: #81A1C1">true</span></span></code></pre>
<p>And they can have nested child nodes, too!</p>
<pre class="shiki" style="background-color: #2e3440ff"><code><span class="line"><span style="color: #81A1C1">contents</span><span style="color: #D8DEE9FF"> {</span></span>
<span class="line"><span style="color: #D8DEE9FF"> </span><span style="color: #81A1C1">section</span><span style="color: #D8DEE9FF"> </span><span style="color: #A3BE8C">&quot;First section&quot;</span><span style="color: #D8DEE9FF"> {</span></span>
<span class="line"><span style="color: #D8DEE9FF"> </span><span style="color: #81A1C1">paragraph</span><span style="color: #D8DEE9FF"> </span><span style="color: #A3BE8C">&quot;This is the first paragraph&quot;</span></span>
<span class="line"><span style="color: #D8DEE9FF"> </span><span style="color: #81A1C1">paragraph</span><span style="color: #D8DEE9FF"> </span><span style="color: #A3BE8C">&quot;This is the second paragraph&quot;</span></span>
<span class="line"><span style="color: #D8DEE9FF"> }</span></span>
<span class="line"><span style="color: #D8DEE9FF">}</span></span></code></pre>
<p>Nodes without children are terminated by a newline, a semicolon, or the end of
a file stream:</p>
<pre class="shiki" style="background-color: #2e3440ff"><code><span class="line"><span style="color: #81A1C1">node1</span><span style="color: #D8DEE9FF">; </span><span style="color: #81A1C1">node2</span><span style="color: #D8DEE9FF">; </span><span style="color: #81A1C1">node3</span><span style="color: #D8DEE9FF">;</span></span></code></pre>
<h3>Values</h3>
<p>KDL supports 4 data types:</p>
<ul>
<li>Strings: <code>&quot;hello world&quot;</code></li>
<li>Numbers: <code>123.45</code></li>
<li>Booleans: <code>true</code> and <code>false</code></li>
<li>Null: <code>null</code></li>
</ul>
<h4>Strings</h4>
<p>It supports two different formats for string input: escaped and raw.</p>
<pre class="shiki" style="background-color: #2e3440ff"><code><span class="line"><span style="color: #81A1C1">node</span><span style="color: #D8DEE9FF"> </span><span style="color: #A3BE8C">&quot;this</span><span style="color: #EBCB8B">\n</span><span style="color: #A3BE8C">has</span><span style="color: #EBCB8B">\t</span><span style="color: #A3BE8C">escapes&quot;</span></span>
<span class="line"><span style="color: #81A1C1">other</span><span style="color: #D8DEE9FF"> </span><span style="color: #A3BE8C">r&quot;C:\Users\zkat\&quot;</span></span></code></pre>
<p>Both types of string can be multiline as-is, without a different syntax:</p>
<pre class="shiki" style="background-color: #2e3440ff"><code><span class="line"><span style="color: #81A1C1">string</span><span style="color: #D8DEE9FF"> </span><span style="color: #A3BE8C">&quot;my</span></span>
<span class="line"><span style="color: #A3BE8C">multiline</span></span>
<span class="line"><span style="color: #A3BE8C">value&quot;</span></span></code></pre>
<p>And for raw strings, you can add any number of # after the r and the last &quot; to
disambiguate literal &quot; characters:</p>
<pre class="shiki" style="background-color: #2e3440ff"><code><span class="line"><span style="color: #81A1C1">other-raw</span><span style="color: #D8DEE9FF"> </span><span style="color: #A3BE8C">r#&quot;hello&quot;world&quot;#</span></span></code></pre>
<h4>Numbers</h4>
<p>There's 4 ways to represent numbers in KDL. KDL does not prescribe any
representation for these numbers, and it's entirely up to individual
implementations whether to represent all numbers with a single type, or to
have different representations for different forms.</p>
<p>KDL has regular decimal-radix numbers, with optional decimal part, as well as
an optional exponent.</p>
<pre class="shiki" style="background-color: #2e3440ff"><code><span class="line"><span style="color: #81A1C1">num</span><span style="color: #D8DEE9FF"> </span><span style="color: #B48EAD">1.234e-42</span></span></code></pre>
<p>And using the appropriate prefix, you can also enter hexadecimal, octal, and
binary literals:</p>
<pre class="shiki" style="background-color: #2e3440ff"><code><span class="line"><span style="color: #81A1C1">my-hex</span><span style="color: #D8DEE9FF"> </span><span style="color: #B48EAD">0xdeadbeef</span></span>
<span class="line"><span style="color: #81A1C1">my-octal</span><span style="color: #D8DEE9FF"> </span><span style="color: #B48EAD">0o755</span></span>
<span class="line"><span style="color: #81A1C1">my-binary</span><span style="color: #D8DEE9FF"> </span><span style="color: #B48EAD">0b10101101</span></span></code></pre>
<p>Finally, all numbers can have underscores to help readability:</p>
<pre class="shiki" style="background-color: #2e3440ff"><code><span class="line"><span style="color: #81A1C1">bignum</span><span style="color: #D8DEE9FF"> </span><span style="color: #B48EAD">1_000_000</span></span></code></pre>
<h3>Comments</h3>
<p>KDL supports C-style comments, both line-based and multiline. Multiline
comments can be nested.</p>
<pre class="shiki" style="background-color: #2e3440ff"><code><span class="line"><span style="color: #616E88">// C style</span></span>
<span class="line"><span style="color: #616E88">/*</span></span>
<span class="line"><span style="color: #616E88">C style multiline</span></span>
<span class="line"><span style="color: #616E88">*/</span></span>
<span class="line"><span style="color: #81A1C1">tag</span><span style="color: #D8DEE9FF"> </span><span style="color: #616E88">/*foo=true*/</span><span style="color: #D8DEE9FF"> </span><span style="color: #8FBCBB">bar</span><span style="color: #ECEFF4">=</span><span style="color: #81A1C1">false</span></span>
<span class="line"><span style="color: #616E88">/*/*</span></span>
<span class="line"><span style="color: #616E88">hello</span></span>
<span class="line"><span style="color: #616E88">*/*/</span></span></code></pre>
<p>On top of that, KDL supports <code>/-</code> &quot;slashdash&quot; comments, which can be used to
comment out individual nodes, arguments, or children:</p>
<pre class="shiki" style="background-color: #2e3440ff"><code><span class="line"><span style="color: #616E88">// This entire node and its children are all commented out.</span></span>
<span class="line"><span style="color: #616E88">/-mynode &quot;foo&quot; key=1 {</span></span>
<span class="line"><span style="color: #616E88"> a</span></span>
<span class="line"><span style="color: #616E88"> b</span></span>
<span class="line"><span style="color: #616E88"> c</span></span>
<span class="line"><span style="color: #616E88">}</span></span>
<span class="line"><span style="color: #81A1C1">mynode</span><span style="color: #D8DEE9FF"> </span><span style="color: #616E88">/-&quot;commented&quot; </span><span style="color: #A3BE8C">&quot;not commented&quot;</span><span style="color: #D8DEE9FF"> </span><span style="color: #616E88">/-key=&quot;value&quot; /-{</span></span>
<span class="line"><span style="color: #616E88"> a</span></span>
<span class="line"><span style="color: #616E88"> b</span></span>
<span class="line"><span style="color: #616E88">}</span></span></code></pre>
<h3>Type Annotations</h3>
<p>KDL supports type annotations on both values and nodes. These can be
arbitrary, but can be used by individual implementations or use-cases to
constrain KDL's basic types. A number of type names are also reserved to have
specific meanings.</p>
<pre class="shiki" style="background-color: #2e3440ff"><code><span class="line"><span style="color: #81A1C1">numbers</span><span style="color: #D8DEE9FF"> </span><span style="color: #81A1C1">(u8)10</span><span style="color: #D8DEE9FF"> </span><span style="color: #81A1C1">(i32)20</span><span style="color: #D8DEE9FF"> </span><span style="color: #8FBCBB">myfloat</span><span style="color: #ECEFF4">=</span><span style="color: #81A1C1">(f32)1.5</span><span style="color: #D8DEE9FF"> {</span></span>
<span class="line"><span style="color: #D8DEE9FF"> </span><span style="color: #81A1C1">strings</span><span style="color: #D8DEE9FF"> </span><span style="color: #81A1C1">(uuid)</span><span style="color: #A3BE8C">&quot;123e4567-e89b-12d3-a456-426614174000&quot;</span><span style="color: #D8DEE9FF"> </span><span style="color: #81A1C1">(date)</span><span style="color: #A3BE8C">&quot;2021-02-03&quot;</span><span style="color: #D8DEE9FF"> </span><span style="color: #8FBCBB">filter</span><span style="color: #ECEFF4">=</span><span style="color: #81A1C1">(regex)r</span><span style="color: #A3BE8C">&quot;$\d+&quot;</span></span>
<span class="line"><span style="color: #D8DEE9FF"> </span><span style="color: #81A1C1">(author)person</span><span style="color: #D8DEE9FF"> </span><span style="color: #8FBCBB">name</span><span style="color: #ECEFF4">=</span><span style="color: #A3BE8C">&quot;Alex&quot;</span></span>
<span class="line"><span style="color: #D8DEE9FF">}</span></span></code></pre>
<h3>More Details</h3>
<pre class="shiki" style="background-color: #2e3440ff"><code><span class="line"><span style="color: #616E88">// Nodes can be separated into multiple lines</span></span>
<span class="line"><span style="color: #81A1C1">title</span><span style="color: #D8DEE9FF"> \</span></span>
<span class="line"><span style="color: #D8DEE9FF"> </span><span style="color: #A3BE8C">&quot;Some title&quot;</span></span>
<span class="line"><span style="color: #616E88">// Files must be utf8 encoded!</span></span>
<span class="line"><span style="color: #81A1C1">smile</span><span style="color: #D8DEE9FF"> </span><span style="color: #A3BE8C">&quot;😁&quot;</span></span>
<span class="line"><span style="color: #616E88">// Instead of anonymous nodes, nodes and properties can be wrapped</span></span>
<span class="line"><span style="color: #616E88">// in &quot;&quot; for arbitrary node names.</span></span>
<span class="line"><span style="color: #A3BE8C">&quot;!@#$@$%Q#$%~@!40&quot;</span><span style="color: #D8DEE9FF"> </span><span style="color: #A3BE8C">&quot;1.2.3&quot;</span><span style="color: #D8DEE9FF"> </span><span style="color: #A3BE8C">&quot;!!!!!&quot;</span><span style="color: #D8DEE9FF">=</span><span style="color: #81A1C1">true</span></span>
<span class="line"><span style="color: #616E88">// The following is a legal bare identifier:</span></span>
<span class="line"><span style="color: #81A1C1">foo123~!@#$%^&amp;*.</span><span style="color: #D8DEE9FF">:&#39;</span><span style="color: #81A1C1">|</span><span style="color: #D8DEE9FF">?</span><span style="color: #81A1C1">+</span><span style="color: #D8DEE9FF"> </span><span style="color: #A3BE8C">&quot;weeee&quot;</span></span>
<span class="line"><span style="color: #616E88">// And you can also use unicode!</span></span>
<span class="line"><span style="color: #81A1C1">ノード</span><span style="color: #D8DEE9FF">　</span><span style="color: #8FBCBB">お名前</span><span style="color: #ECEFF4">=</span><span style="color: #A3BE8C">&quot;☜(ﾟヮﾟ☜)&quot;</span></span>
<span class="line"><span style="color: #616E88">// kdl specifically allows properties and values to be</span></span>
<span class="line"><span style="color: #616E88">// interspersed with each other, much like CLI commands.</span></span>
<span class="line"><span style="color: #81A1C1">foo</span><span style="color: #D8DEE9FF"> </span><span style="color: #8FBCBB">bar</span><span style="color: #ECEFF4">=</span><span style="color: #81A1C1">true</span><span style="color: #D8DEE9FF"> </span><span style="color: #A3BE8C">&quot;baz&quot;</span><span style="color: #D8DEE9FF"> </span><span style="color: #8FBCBB">quux</span><span style="color: #ECEFF4">=</span><span style="color: #81A1C1">false</span><span style="color: #D8DEE9FF"> </span><span style="color: #B48EAD">1</span><span style="color: #D8DEE9FF"> </span><span style="color: #B48EAD">2</span><span style="color: #D8DEE9FF"> </span><span style="color: #B48EAD">3</span></span></code></pre>
</section>
<section class="kdl-section" id="implementations">
<h2>Implementations</h2>
<ul>
<li>Rust: <a href="https://github.com/kdl-org/kdl-rs">kdl-rs</a>, <a href="https://crates.io/crates/knuffel/">knuffel</a> (latter includes derive macro), and <a href="https://github.com/Lucretiel/kaydle">kaydle</a> (serde-based)</li>
<li>JavaScript: <a href="https://github.com/kdl-org/kdljs">kdljs</a>, <a href="https://github.com/virtualstate/kdl">@virtualstate/kdl</a> (query only, JSX based)</li>
<li>Ruby: <a href="https://github.com/danini-the-panini/kdl-rb">kdl-rb</a></li>
<li>Dart: <a href="https://github.com/danini-the-panini/kdl-dart">kdl-dart</a></li>
<li>Java: <a href="https://github.com/hkolbeck/kdl4j">kdl4j</a></li>
<li>PHP: <a href="https://github.com/kdl-org/kdl-php">kdl-php</a></li>
<li>Python: <a href="https://github.com/tabatkins/kdlpy">kdl-py</a>, <a href="https://github.com/djmattyg007/python-cuddle">cuddle</a>, <a href="https://github.com/tjol/ckdl">ckdl</a></li>
<li>Elixir: <a href="https://github.com/IceDragon200/kuddle">kuddle</a></li>
<li>XSLT: <a href="https://github.com/Devasta/XML2KDL">xml2kdl</a></li>
<li>Haskell: <a href="https://github.com/fuzzypixelz/Hustle">Hustle</a></li>
<li>.NET: <a href="https://github.com/oledfish/Kadlet">Kadlet</a></li>
<li>C: <a href="https://github.com/tjol/ckdl">ckdl</a></li>
<li>C++: <a href="https://github.com/tjol/ckdl">kdlpp</a> (part of ckdl, requires C++20)</li>
<li>OCaml: <a href="https://github.com/Bannerets/ocaml-kdl">ocaml-kdl</a></li>
<li>Nim: <a href="https://github.com/Patitotective/kdl-nim">kdl-nim</a></li>
<li>Common Lisp: <a href="https://github.com/chee/kdlcl">kdlcl</a></li>
<li>Go: <a href="https://github.com/lunjon/gokdl">gokdl</a></li>
</ul>
<h2>Editor Support</h2>
<ul>
<li><a href="https://marketplace.visualstudio.com/items?itemName=kdl-org.kdl&amp;ssr=false#review-details">VS Code</a></li>
<li><a href="https://packagecontrol.io/packages/KDL">Sublime Text</a></li>
<li><a href="https://plugins.jetbrains.com/plugin/20136-kdl-document-language">Intellij IDEA</a></li>
<li><a href="https://github.com/imsnif/kdl.vim">vim</a></li>
</ul>
</section>
<section class="kdl-section" id="design-and-discussion">
<h2>Design and Discussion</h2>
<p>KDL is still extremely new, and discussion about the format should happen over
on the <a href="https://github.com/kdl-org/kdl/discussions">discussions</a> page in the
Github repo. Feel free to jump in and give us your 2 cents!</p>
</section>
<section class="kdl-section" id="design-principles">
<h2>Design Principles</h2>
<ol>
<li>Maintainability</li>
<li>Flexibility</li>
<li>Cognitive simplicity and Learnability</li>
<li>Ease of de/serialization</li>
<li>Ease of implementation</li>
</ol>
</section>
<section class="kdl-section" id="compatibility-with-json-and-xml">
<h2>Compatibility with JSON and XML</h2>
<p>There are two specifications for writing KDL that can be losslessly translated
between it and JSON or XML. These specifications define a stricter <em>subset</em> of
KDL that, even if not entirely idiomatic, is still valid and fits into the
data models of the other two languages:</p>
<ul>
<li><a href="https://github.com/kdl-org/kdl/blob/main/JSON-IN-KDL.md">JSON in KDL</a></li>
<li><a href="https://github.com/kdl-org/kdl/blob/main/XML-IN-KDL.md">XML in KDL</a></li>
</ul>
</section>
<section class="kdl-section" id="faq">
<h2>FAQ</h2>
<h4>How do you pronounce KDL?</h4>
<p>Same as &quot;cuddle&quot;.</p>
<h4>Why yet another document language?</h4>
<p>Because nothing out there felt quite right. The closest one I found was
SDLang, but that had some design choices I disagreed with.</p>
<h4>Ok, then, why not SDLang?</h4>
<p>SDLang is designed for use cases that are not interesting to me, but are very
relevant to the D-lang community. KDL is very similar in many ways, but is
different in the following ways:</p>
<ul>
<li>The grammar and expected semantics are <a href="https://github.com/kdl-org/kdl/blob/main/SPEC.md">well-defined and specified</a>.</li>
<li>There is only one &quot;number&quot; type. KDL does not prescribe representations.</li>
<li>Slashdash (<code>/-</code>) comments are great and useful!</li>
<li>I am not interested in having first-class date types, and SDLang's are very
non-standard.</li>
<li>Values and properties can be interspersed with each other, rather than one
having to follow the other.</li>
<li>KDL does not have a first-class binary data type. Just use strings with base64.</li>
<li>All strings in KDL are multi-line, and raw strings are written with
Rust-style syntax (<code>r&quot;foo&quot;</code>), instead of backticks.</li>
<li>KDL identifiers can use UTF-8 and are much more lax about symbols than SDLang.</li>
<li>KDL does not support &quot;anonymous&quot; nodes.</li>
<li>Instead, KDL supports arbitrary identifiers for node names and attribute
names, meaning you can use arbitrary strings for those: <code>&quot;123&quot; &quot;value&quot;=1</code> is
a valid node, for example. This makes it easier to use KDL for
representing arbitrary key/value pairs.</li>
</ul>
<h4>Have you seen that one XKCD comic about standards?</h4>
<p>Yes. I have. Please stop linking me to it.</p>
<h4>What about YAML?</h4>
<p>YAML is a great, widespread language. Unlike KDL, which is node-based (like
XML or HTML), it's based on map and array data structures, which can provide
an easier serialization experience in some cases.</p>
<p>At the same time, YAML can be ambiguous about what types the data written into
it is. There's also a persistent issue where very large YAML files become
unmanageable, especially due to the significant indentation feature.</p>
<p>KDL is designed to avoid these particular pitfalls by always being explicit
about types, and having clearly-delimited scope (and the ability to
auto-indent/auto-format). Syntax errors are easier to catch, and large files
are (hopefully!) much more manageable.</p>
<h4>What about JSON?</h4>
<p>JSON is a great serialization language, but it can be very difficult to use as
a human configuration language. This is largely due to its very specific, very
strict syntax, as well as its lack of support for comments.</p>
<p>KDL, on the other hand, has great comment support, and has a much more
forgiving syntax without being so flexible as to allow certain classes of
unfortunate mistakes. It also has much more flexibility around how to
represent data.</p>
<p>If you need to interoperate with a service that consumes or emits JSON, or for
some other reason have need to write &quot;JSON in KDL&quot;, <a href="https://github.com/kdl-org/kdl/blob/main/JSON-IN-KDL.md">we have JiK, an official
microsyntax for losslessly encoding JSON</a>.</p>
<h4>What about TOML?</h4>
<p>It nests very poorly. It doesn't fare well with large files.</p>
<h4>What about XML?</h4>
<p>XML is actually pretty fantastic, and has long been a standard for data
exchange across many industries. At the same time, XML is known to be very
verbose, and editing it involves writing (and updating) matching tags. Another
large pitfall with XML is its lack of direct support for arbitrary string
key/value pairs, so what would be a simple <code>foo: x</code> in some languages has to
be represented as <code>&lt;entry name=&quot;foo&quot; value=&quot;x&quot; /&gt;</code> or something similar. XML
also functions great as a <strong>markup</strong> language. That is, it is easy to
intersperse with text, like HTML.</p>
<p>KDL, just like XML, is a node/element-based language, but with much more
lightweight syntax. It also adds the ability to apply anonymous values
directly to a node, rather than as children. That is, <code>nodename 1 2 3</code> instead
of <code>&lt;element&gt;&lt;child&gt;1&lt;/child&gt;&lt;child&gt;2&lt;/child&gt;(etc)&lt;/element&gt;</code>. This can make
it much more manageable and readable as a human configuration language, and is
also less verbose when exchanging documents across APIs!</p>
<p>Finally, KDL is <strong>not</strong> a markup language. XML or HTML do a much better job of
&quot;marking up&quot; a text document with special tags, although KDL can still be
useful for templating engines that want to be more strict about text
fragments.</p>
<p>If you need to interoperate with a service that consumes or emits XML, or for
some other reason have need to write &quot;XML in KDL&quot;, <a href="https://github.com/kdl-org/kdl/blob/main/XML-IN-KDL.md">we have XiK, an official
microsyntax for losslessly encoding XML</a>.</p>
</section>
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