WASM Binary Analyzer

A WebAssembly (WASM) binary is a compact binary format that encodes a WebAssembly module as a sequence of sections. Each section has a type ID, a byte length, and a payload. The WASM binary format defines 13 standard section types — from the Type section (function signatures) to the Code section (function bytecode) and Data section (linear memory initializers). Additionally, compilers add Custom sections (ID 0) for debug information, source maps, and tool metadata. Our wasm binary analyzer parses the binary format directly in your browser, reads each section header and size, and presents a visual breakdown of which sections contribute most to file size — helping you identify optimization opportunities.

1. 1Upload your .wasm file: Drag and drop your WebAssembly binary onto the drop zone or click to browse. The file is read as an ArrayBuffer in your browser — no data is sent to any server. Any valid WASM binary (version 1) is supported.
2. 2Click "Analyze WASM": The analyzer validates the magic number (\0asm) and version, then iterates through all sections reading their IDs and sizes using LEB128 variable-length integer decoding. Custom section names are extracted to identify debug sections. Processing runs entirely in your browser.
3. 3Review the analysis: The results show a file summary, stacked bar chart of section sizes, a sortable section table with descriptions, debug section warnings, and actionable wasm-opt optimization commands.

• Code Section (§10): Contains the bytecode for all function bodies — typically the largest section in optimized WASM binaries. Reducible with wasm-opt -O3.
• Data Section (§11): Contains linear memory initializers — static data like string literals, lookup tables, and embedded assets. Large data sections suggest embedded binary assets that could be loaded separately.
• Custom Sections (§0): Named sections added by compilers — includes .debug_* DWARF debug info, name (function names), producers (build tool metadata), and sourceMappingURL. These are safe to strip for production.
• Import/Export Sections (§2, §7): Define the interface between WASM and JavaScript — imported functions, memories, and globals, plus exported symbols. Large import sections may indicate excessive JS/WASM boundary crossings.

The most impactful WASM size reduction steps are: (1) strip debug sections with wasm-opt --strip-debug — debug info can be 50–80% of an unoptimized binary; (2) optimize the code section with wasm-opt -O3 — typically achieves 10–30% code section reduction; (3) serve with Brotli compression — WASM files compress 60–80% with Brotli, making the transfer size much smaller than the on-disk size. The wasm binary analyzer shows the uncompressed section sizes — multiply by ~0.25 for an estimate of Brotli-compressed transfer size.