If you have written sensitive files to .cursorignore and find that the Cursor Agent may still encounter them, this is usually not an ignore failure, but rather a larger scope of its scope. According to Cursor's official documentation, .cursorignore mainly restricts code access at the index, tab, agent edit, inline edit, and reference levels, but terminal calls and MCP tool calls initiated by agents are not completely blocked by .cursorignore.
This is very important, because many people think of .cursorignore as an "absolute isolation layer". It's actually more like AI contextual access control than an OS-level sandbox. As long as you can see these files in your terminal, in your local tools, in the MCP server itself, it's not surprising that the agent gets the content indirectly through those links.
So the correct understanding should be:
1. .cursorignore is suitable for reducing index noise and reducing the AI default visibility range.
2. It helps with security, but it is not a complete security perimeter.
3. When it comes to truly sensitive content such as API keys, certificates, and production keys, you can't rely solely on .cursorignore.
The more stable treatment usually has three layers. The first layer moves sensitive content from warehouses and workspaces, or hosts it with environment variables and key management tools. The second layer reduces terminal visibility by means of system permissions, directory isolation, and separate warehouses. The third level is to check which paths you can access to the MCP tools and scripts you have accessed.
Another myth is that "since the official default ignores .env, it is safe". It is not. The official documentation itself reminds that due to the unpredictability of large models themselves, ignore is not a complete protection. It reduces the probability of exposure, but is not a subscenium for true key governance.
If your goal is just to keep Cursor from indexing certain large directories, .cursorignore is very useful; But if your goal is to "not be seen by the agent anyway", then you should escalate the policy to the system and tool permissions layer instead of continuing to add tricks to the ignore rule.
In a word, .cursorignore manages the default access to many AI functions, not the final access to all execution links. Don't rely on it to guard the door for something that is really sensitive.
