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<h1>WebAssembly Specifications</h1>

To support the <em>embedding</em> of WebAssembly into different environments, its specification is split into <em>layers</em> that are specified in separate documents.

Source for these documents is available

<a href="https://github.com/WebAssembly/spec/">here</a>.

<h3>Core Specification</h3>

<p>Defines the semantics of WebAssembly modules independent from a concrete embedding.

The WebAssembly core is specified in a single document:</p>

<ul>

<li>

<p><b>WebAssembly</b>:

defines the structure of WebAssembly modules, their instruction set, and their representation

in binary and text format, as well as the semantics of validation,

instantiation, and execution.

</p>

<ul>

<li><a href="core/">Browser version</a> (multi-page)</li>

<li><a href="core/bikeshed/">W3C version</a> (single-page)</li>

<li><a href="core/_download/WebAssembly.pdf">PDF version</a></li>

<!-- <li><a href="https://github.com/WebAssembly/spec/document/core/">Sources</a></li> -->

</ul>

</li>

</ul>

<h3>Embedder Specifications</h3>

<p>Define <em>application programming interfaces</em> (APIs) enabling the use of WebAssembly modules in concrete embedding environments.

Currently, two APIs are specified:</p>

<li><p><b>JavaScript Embedding</b>: defines JavaScript classes and objects for accessing WebAssembly from within JavaScript, including methods for validation, compilation, instantiation, and classes for representing and manipulating imports and exports as JavaScript objects.</p>

<ul>

<li><a href="js-api/">W3C version</a></li>

<!-- <li><a href="https://github.com/WebAssembly/spec/document/js-api/">Sources</a></li> -->

</ul>

</li>

<li><p><b>Web Embedding</b>: defines extensions to the JavaScript API made available specifically in web browsers, in particular, an interface for streaming compilation and instantiation from origin-bound <code>Response</code> types.</p>

<ul>

<li><a href="web-api/">W3C version</a></li>

<!-- <li><a href="https://github.com/WebAssembly/spec/document/web-api/">Sources</a></li> -->

</ul>

</li>

<h3>Metadata specifications</h3>

<p>Define the format and semantics of extra information attached to a WebAssembly module</p>

<ul>

<li><p><b>Code Metadata</b>: defines metadata attached to instructions</p>

<ul>

<li><a href="metadata/code/">Browser version</a></li>

<li><a href="metadata/code/_download/WebAssembly-Metadata-Code.pdf">PDF version</a></li>

</ul>

</li>

</ul>

<h3>Legacy Extensions</h3>

<p>Define extensions that are deprecated, but may still be in use.</p>

<ul>

<li><p><b>Legacy Exception Handling</b>: defines additional instructions for exception handling that may still be available in some engines and tools, specifically web browsers.</p>

<ul>

<li><p><b>Core specification</b></p>

<ul>

<li><a href="legacy/exceptions/core/">Browser version</a></li>

<li><a href="legacy/exceptions/core/_download/WebAssembly-Legacy-Exceptions.pdf">PDF version</a></li>

</ul>

</li>

<li><p><b>JavaScript Embedding</b></p>

<ul>

<li><a href="legacy/exceptions/js-api/">W3C version</a></li>

</ul>

</li>

</ul>

</li>

</ul>

<h3>All Versions</h3>

<li><a href="versions/core/WebAssembly-1.0.pdf">WebAssembly 1.0</a> (2017)</li>

<li><a href="versions/core/WebAssembly-2.0.pdf">WebAssembly 2.0</a> (2022)</li>

<li><a href="versions/core/WebAssembly-3.0.pdf">WebAssembly 3.0</a> (2025)</li>