diff --git a/README.md b/README.md
index dfc3613..fbdc2bf 100644
--- a/README.md
+++ b/README.md
@@ -7,6 +7,8 @@ This project started because I dislike GNU enough to do something about it.  All
 
 The first and primary goal is to build a statically-linkable, fully portable binary userland distribution not dissimilar to busybox.
 
+The compatibility spec is considered to be the source code of the tools located in the [illumos-gate](https://github.com/illumos/illumos-gate/tree/master/usr/src/cmd) repo.  Not all tools will be implemented, as they are very specific to illumos.
+
 ## Project Layout
 
 In the root of the repo there is `Cargo.toml`, which is the workspace definition for the rest of the project.  From here, you could run `cargo build` and build all the tools at once.