glsl-optimizer | GLSL optimizer based on Mesa 's GLSL compiler

"Minification" is something different to optimization. Typically the term is used to describe a process that takes a source file in text form and removes all superfluous whitespace and replaces all identifiers with shorter ones.

Strictly speaking the whole idea of minification is a folly, since it has zero impact on performance; neither lexing the code, nor the compilation result are affected by it. The whole minification doofus started in web development to reduce webpage resource size; totally worthless, because you'll get far better performance if you just compress the text with gzip or similar. Heck after zipping the original and the minified versions' sized will probably within a few bytes of each other.

If you're really concerned about the size of your shader as a resource, just compress it (but mind the overhead of the decompression code). EDIT: However if your target is WebGL, then make use of HTTP transport gzip compression. The relevant browsers do support it all, and most HTTP servers can be configured to transparently deliver a supplementary .gz suffixed file (or do the compression and cache it on the fly).

For optimization, you should look to the other offerings of Khronos. Specifically the GLSL to SPIR-V compiler glslc, the SPIR-V optimizer spirv-opt, and the SPIR-V decompiler spirv-cross. You can chain those up to create optimized, "reduced" GLSL.