Performance

This page describes a few topics around Knip’s performance, and how you might improve it.

Knip does not want to tell you how to structure files or how to write your code, but it might still be good to understand inefficient patterns for Knip.

Use the --debug and --performance flags to find potential bottlenecks.

Cache

Use --cache to speed up consecutive runs.

Ignoring files

Files matching the ignore patterns are not excluded from the analysis. They’re just not printed in the report. Use negated entry and project patterns to exclude files from the analysis.

Read configuring project files for details and examples. Improving configuration may have a significant impact on performance.

Workspace sharing

Knip shares files from separate workspaces if the configuration in tsconfig.json allows this. This aims to reduce memory consumption and run duration. Relevant compiler options include baseUrl, paths and moduleResolution.

With the --debug flag you can see how many programs Knip uses. Look for messages like this:

...
[*] Installed 2 programs for 29 workspaces
...
[*] Analyzing used resolved files [P1/1] (123)
...
[*] Analyzing used resolved files [P1/2] (8)
...
[*] Analyzing used resolved files [P2/1] (41)
...

The first number in P1/1 is the number of the programs, the second number indicates additional entry files were found so it does another round of analysis on those files.

Use —isolate-workspaces to disable this behavior. This is usually not necessary, but more of an escape hatch in cases with memory usage issues or incompatible compilerOptions across workspaces. Workspaces are analyzed sequentially to spread out memory usage more evenly, which may prevent crashes on large monorepos.

Language Service

Knip does not install the TypeScript Language Service (LS) by default. This is expensive, as TypeScript needs to set up symbols and caching for the rather slow findReferences function.

There are two cases that enforce Knip to install the LS.

1. Class members

The findReferences function is used to find unused members of imported classes (i.e. when the issue type classMembers is included).

2. Include external type definitions

When --include-libs is enabled, Knip enables loading type definitions of external dependencies. This will also install the LS to access its findReferences function. It acts as an extra line of defense: only exports that weren’t referenced to during default procedure go through this.

Metrics

Use the --performance flag to see how many times potentially expensive functions (e.g. findReferences) are invoked and how much time is spent in those functions. Example usage:

knip --include classMembers --performance

A last resort

In case Knip is unbearably slow (or even crashes), you could resort to lint individual workspaces.