In Cursor, .cursorignore and .cursorindexingignore look similar, but they don't serve the same purpose. Many large repositories mix the two from the beginning, and the result is either indexing or messing, or blocking the code that was originally intended to be seen by AI.
The simplest difference is that .cursorindexingignore only affects the index and does not affect most AI read power, while .cursorignore is more aggressive, preventing these files from entering the index and also affecting access paths such as Tab, Agent, Inline Edit, and references. That is, one is performance and search, and the other is access control.
If you want to make the codebase search cleaner and faster because the monorepo is too large, too many compilation products, and the documentation is too cluttered, use .cursorindexingignore first. Because these documents may not be worth indexing, you don't necessarily want to completely prohibit AI from viewing them when necessary.
Conversely, if you explicitly do not want certain directories to enter the AI routine workflow, such as credentials, private configurations, and extraneous subprojects, then .cursorignore is more suitable. It says "don't let this content enter the main AI access surface", not just "don't embedding them".
Why do many people use reverse? Because when you see "ignore", you will understand it as a meaning by default. As a result, the performance problem is treated as a security issue, or the security problem is treated as an index problem. Typical consequences are:
1. Using .cursorignore to block a bunch of large directories that you don't want to index, resulting in a narrow range of visibility when the AI answers.
2. Only write .cursorindexingignore, thinking that sensitive files have been blocked, but the actual AI may still encounter it in other paths.
In practice, a very useful division is: spawn, cache, huge logs, and third-party vendor packages, with priority placed in .cursorindexingignore; If you really don't want to enter the content in the regular AI context, then add .cursorignore. After writing, go to Cursor's Indexing & Docs to look at included files, or use git check-ignore to check the rules, don't rely on guesswork.
So these two documents are not who replaces whom, but each has its own layer. The more complex the large repository, the more it should separate "for speeding up indexing" and "for reducing exposure pipe access" from the beginning. I can't tell this clearly, and the more I tune it up, the more chaotic it becomes.
