Tools I use and recommend

BundlephobiaShows how much size is particular NPM package after including it in your bundle
CDN FinderShow CDN used on website, easily visible
FontdropOptimize font by turning off features, visualization real time
GlyphhangerOptimize fonts, subset
Google Devs ShowcaseGoogle use cases of performance optimizations
Google Webfonts HelperQuickly download google webfonts in various variants and formats, with @font-face
GTMetrixTool for auditing website performance. Has waterfall
IdentifontVisually compare two fonts and see the difference
ImageoptimMac app to optimize your images
KrakenCompress bitmaps
PageSpeed InsightsGoogle lighthouse report
RedbotAudit headers and their syntax
Remove BGRemove BG from bitmap
Request mapVisualize request map to show how long are the request chains
Request mapShow request map for the website
SitespeedRun your own scheduled performance testing and compare competitors
SSL TestAudit SSL parameters, warn about security issues
SubsetterSubsets fonts online
SVG to PNGThe best tool to rasterize SVGs
SVGOMGOptimize SVG image with live preview
Timeline ViewerView and compare Chrome Devtools timelines to detect improvements and regressions
TinyPNGCompress bitmaps
Wakamai FondueDetect if your font is variable (can be bold/light without loading additional variants)
WebpagetestBest waterfalls on the market. Blocking 3rd party (or any other resource) experiments. Comparisons of two tests (ie. before and after)
Website CarbonShows how much carbon is generated to enter your website
WPO StatsBusiness case studies of performance optimizations
Yellowlab ToolsVery fast, easy to understand and actionable performance report