The WebGL shader validator plugin for Sublime Text 2 that +Paul Lewis
and I built is now in Package Control! If you have Package Control installed, just "Install Package" and look for "GL Shader Validator". Otherwise, you can still download the repo and install it as you would any other package. When you save a file, any errors will be highlighted (see below for current limitations).
If you have any problems, please file an issue on the github project so we can fix it.
How it works: The heavy lifting is done by the preprocessor and verifier from the ANGLE project. This does the validation itself, which means you get the exact same error checking you get in Chrome and Firefox, but without requiring a page refresh just to see if you made a syntax error or spelling mistake (and refreshes can be super annoying when also loading a bunch of WebGL assets).
The great thing about using ANGLE for validation is that it will make sure your shader is fully conformant with the WebGL spec* (which has requirements beyond just valid GLSL) and there are several groups -- including two major browser vendors -- that are very motivated to fix bugs and ensure it remains conformant.
Current limitations: file names have to end with a '.vert' or '.frag' file extension, and you have to have some form of GLSL syntax highlighting enabled for the file within Sublime (the "OpenGL Shading Language" package in Package Control works well). We recognize that many people don't organize their shader files like this: some use inline strings, some concatenate their vert and frag shaders in a single file (with shared common code). We want this to be a useful plugin, so we're eager to expand support for other shader format preferences. Please file an issue on the project with specifics about your approach (patches are even more welcome :) and we'll see what we can do.
[*] ANGLE actually supports several different GLSL-variant specs, including regular GLSL ES and the proposed variant for CSS Shaders. See the package's User settings for how to select other specs to validate against.