Sometimes ESLint can take a while a run, especially if you have a lot of rules and files. So how do you benchmark how long each rule takes?

With the environment variable TIMING, ESLint tracks the performance of individual rules.

So instead of running ESLint like:

npx eslint ./lib/

Prepend the command with TIMING=1:

TIMING=1 npx eslint ./lib/

Rule                    | Time (ms) | Relative
:-----------------------|----------:|--------:
prettier/prettier       |   136.659 |    92.4%
no-unused-vars          |     2.139 |     1.4%
no-redeclare            |     1.780 |     1.2%
no-unexpected-multiline |     0.789 |     0.5%
no-global-assign        |     0.630 |     0.4%
constructor-super       |     0.369 |     0.2%
no-unsafe-finally       |     0.323 |     0.2%
no-unreachable          |     0.319 |     0.2%
no-self-assign          |     0.311 |     0.2%
no-dupe-else-if         |     0.291 |     0.2%

With Yarn, you can get the total time elapsed:

TIMING=1 yarn eslint ./lib/

$ yarn run v1.22.10
/Users/remarkablemark/html-react-parser/node_modules/.bin/eslint ./lib/
Rule                    | Time (ms) | Relative
:-----------------------|----------:|--------:
prettier/prettier       |   140.710 |    92.2%
no-unused-vars          |     2.573 |     1.7%
no-redeclare            |     1.748 |     1.1%
no-unexpected-multiline |     0.845 |     0.6%
no-global-assign        |     0.769 |     0.5%
constructor-super       |     0.377 |     0.2%
no-unreachable          |     0.333 |     0.2%
no-unsafe-finally       |     0.329 |     0.2%
no-dupe-else-if         |     0.287 |     0.2%
no-this-before-super    |     0.283 |     0.2%
✨  Done in 0.81s.