diff --git a/shell.nix b/shell.nix
index c0ff8bc..0d91a51 100644
--- a/shell.nix
+++ b/shell.nix
@@ -1,4 +1,4 @@
 let
-  dev = (import ./src/core/importAtom.nix) { } ./src/dev.toml;
+  dev = (import ./src/core/importAtom.nix) { } ./src/dev.atom;
 in
 dev.shell
diff --git a/src/core.toml b/src/core.atom
similarity index 100%
rename from src/core.toml
rename to src/core.atom
diff --git a/src/core/compose.nix b/src/core/compose.nix
index d4c449b..6a1cef7 100644
--- a/src/core/compose.nix
+++ b/src/core/compose.nix
@@ -55,30 +55,31 @@
 */
 let
   l = builtins;
-  src = import ./mod.nix;
+  core = import ./mod.nix;
 in
 {
+  src,
+  root,
   config,
   extern ? { },
   features ? [ ],
   # internal features of the composer function
-  stdFeatures ? src.stdToml.features.default or [ ],
-  coreFeatures ? src.coreToml.features.default,
+  stdFeatures ? core.stdToml.features.default or [ ],
+  coreFeatures ? core.coreToml.features.default,
   # enable testing code paths
   __internal__test ? false,
   __isStd__ ? false,
 }:
-dir':
 let
-  par = src.prepDir dir';
+  par = (root + "/${src}");
 
-  std = src.importStd {
+  std = core.importStd {
     features = stdFeatures;
     inherit __internal__test;
-  } ../std.toml;
+  } ../std.atom;
 
-  coreFeatures' = src.features.resolve src.coreToml.features coreFeatures;
-  stdFeatures' = src.features.resolve src.stdToml.features stdFeatures;
+  coreFeatures' = core.features.resolve core.coreToml.features coreFeatures;
+  stdFeatures' = core.features.resolve core.stdToml.features stdFeatures;
 
   __atom = config // {
     features = config.features or { } // {
@@ -90,7 +91,7 @@ let
     };
   };
 
-  msg = src.errors.debugMsg config;
+  msg = core.errors.debugMsg config;
 
   f =
     f: pre: dir:
@@ -104,9 +105,9 @@ let
 
       scope =
         let
-          scope' = with src; {
+          scope' = with core; {
             inherit __atom;
-            mod = self';
+            mod = modScope;
             builtins = std;
             import = errors.import;
             scopedImport = errors.import;
@@ -119,7 +120,7 @@ let
             __getFlake = errors.import;
           };
 
-          scope'' = src.set.inject scope' [
+          scope'' = core.set.inject scope' [
             preOpt
             {
               _if = !__isStd__ && l.elem "std" coreFeatures';
@@ -127,7 +128,7 @@ let
             }
             {
               _if = !__isStd__;
-              atom = atom';
+              atom = atomScope;
             }
             {
               _if = __isStd__;
@@ -141,7 +142,8 @@ let
                 # a copy of the global scope, for testing if values exist
                 # for our internal testing functions
                 scope = scope'';
-                inherit src __isStd__ __internal__test;
+                inherit __isStd__ __internal__test;
+                src = core;
               };
             }
           ];
@@ -153,59 +155,69 @@ let
       g =
         name: type:
         let
-          path = src.path.make dir name;
-          file = src.file.parse name;
+          path = core.path.make dir name;
+          file = core.file.parse name;
           member = Import (l.path { inherit path name; });
-          module = src.path.make path "mod.nix";
+          module = core.path.make path "mod.nix";
         in
         if type == "directory" && l.pathExists module then
-          { ${name} = f ((src.lowerKeys self) // src.set.when preOpt) path; }
+          { ${name} = f ((core.lowerKeys mod) // core.set.when preOpt) path; }
         else if type == "regular" && file.ext or null == "nix" && name != "mod.nix" then
           {
             ${file.name} =
               let
-                trace = src.errors.modPath par dir;
+                trace = core.errors.modPath par dir;
               in
-              src.errors.context (msg "${trace}.${file.name}") member;
+              core.errors.context (msg "${trace}.${file.name}") member;
           }
         else
           null # Ignore other file types
       ;
 
-      self' = src.lowerKeys (l.removeAttrs self [ "mod" ] // { outPath = src.rmNixSrcs dir; });
+      modScope = core.lowerKeys (l.removeAttrs mod [ "mod" ] // { outPath = core.rmNixSrcs dir; });
 
-      self =
+      mod =
         let
-          path = src.path.make dir "mod.nix";
+          path = core.path.make dir "mod.nix";
           module = Import (
             l.path {
               inherit path;
               name = baseNameOf path;
             }
           );
-          trace = src.errors.modPath par dir;
+          trace = core.errors.modPath par dir;
         in
-        assert src.modIsValid module dir;
-        src.filterMap g contents // (src.errors.context (msg trace) module);
+        assert core.modIsValid module dir;
+        core.filterMap g contents // (core.errors.context (msg trace) module);
 
     in
-    if src.hasMod contents then
-      src.collectPublic self
+    if core.hasMod contents then
+      core.collectPublic mod
     else
       # Base case: no module
       { };
 
-  atom' = l.removeAttrs (extern // atom // { inherit extern; }) [
-    "atom"
-    (baseNameOf par)
-  ];
+  atomScope =
+    l.removeAttrs
+      (
+        extern
+        // atom
+        // {
+          inherit extern;
+          outPath = core.rmAtomSrc root config.atom.id src;
+        }
+      )
+      [
+        "atom"
+        (baseNameOf par)
+      ];
 
   atom =
     let
-      fixed = src.fix f null par;
+      fixed = core.fix f null par;
     in
-    src.set.inject fixed [
-      ({ _if = __isStd__; } // src.pureBuiltinsForStd fixed)
+    core.set.inject fixed [
+      ({ _if = __isStd__; } // core.pureBuiltinsForStd fixed)
       {
         _if = __isStd__ && l.elem "lib" __atom.features.resolved.atom;
         inherit (extern) lib;
@@ -221,7 +233,7 @@ in
 assert
   !__internal__test
   # older versions of Nix don't have the `warn` builtin
-  || src.errors.warn ''
+  || core.errors.warn ''
     in ${toString ./default.nix}:
     Internal testing functionality is enabled via the `__test` boolean.
     This should never be `true` except in internal test runs.
diff --git a/src/core/importAtom.nix b/src/core/importAtom.nix
index 16306ef..77f6582 100644
--- a/src/core/importAtom.nix
+++ b/src/core/importAtom.nix
@@ -44,7 +44,13 @@ let
   backend = config.backend or { };
   nix = backend.nix or { };
 
-  root = builtins.seq id (atom.path or id);
+  root = mod.prepDir (dirOf path);
+  src = builtins.seq id (
+    let
+      file = mod.parse (baseNameOf path);
+    in
+    file.name
+  );
   extern =
     let
       fetcher = nix.fetcher or "native"; # native doesn't exist yet
@@ -88,7 +94,13 @@ let
 
 in
 mod.compose {
-  inherit extern __internal__test config;
+  inherit
+    extern
+    __internal__test
+    config
+    root
+    src
+    ;
   features = features';
   coreFeatures =
     let
@@ -102,4 +114,4 @@ mod.compose {
     mod.features.resolve mod.stdToml.features feat;
 
   __isStd__ = meta.__is_std__ or false;
-} (dirOf path + "/${root}")
+}
diff --git a/src/core/mod.nix b/src/core/mod.nix
index 36294fa..8e46fe8 100644
--- a/src/core/mod.nix
+++ b/src/core/mod.nix
@@ -15,12 +15,13 @@ let
     std = builtins;
     mod = scopedImport { inherit std mod; } ../std/string/mod.nix;
   } ../std/string/toLowerCase.nix;
-  stdToml = l.fromTOML (l.readFile ../std.toml);
-  coreToml = l.fromTOML (l.readFile ../core.toml);
+  stdToml = l.fromTOML (l.readFile ../std.atom);
+  coreToml = l.fromTOML (l.readFile ../core.atom);
 in
 rec {
   inherit
     fix
+    parse
     filterMap
     stdFilter
     stdToml
@@ -71,6 +72,18 @@ rec {
       );
     };
 
+  rmAtomSrc =
+    path: name: src:
+    l.path {
+      inherit name path;
+      filter =
+        path: type:
+        let
+          file = parse path;
+        in
+        file.name != src;
+    };
+
   importStd = opts: importAtom { inherit (opts) __internal__test features; };
 
   modIsValid =
diff --git a/src/dev.toml b/src/dev.atom
similarity index 100%
rename from src/dev.toml
rename to src/dev.atom
diff --git a/src/std.toml b/src/std.atom
similarity index 100%
rename from src/std.toml
rename to src/std.atom
diff --git a/test/features/recursive-features-loop.toml b/test/features/recursive-features-loop.atom
similarity index 100%
rename from test/features/recursive-features-loop.toml
rename to test/features/recursive-features-loop.atom
diff --git a/test/features/recursive-features.toml b/test/features/recursive-features.atom
similarity index 100%
rename from test/features/recursive-features.toml
rename to test/features/recursive-features.atom
diff --git a/test/features/resolve.nix b/test/features/resolve.nix
index 15b4d30..9e75d42 100644
--- a/test/features/resolve.nix
+++ b/test/features/resolve.nix
@@ -2,6 +2,6 @@ let
   f = import ../../src/core/importAtom.nix { __internal__test = true; };
 in
 {
-  recursive-features = f ./recursive-features.toml;
-  recursive-features-loop = f ./recursive-features-loop.toml;
+  recursive-features = f ./recursive-features.atom;
+  recursive-features-loop = f ./recursive-features-loop.atom;
 }
diff --git a/test/integrity/bld.toml b/test/integrity/bld.atom
similarity index 100%
rename from test/integrity/bld.toml
rename to test/integrity/bld.atom
diff --git a/test/integrity/bld.nix b/test/integrity/bld.nix
index 966d201..7c2ff07 100644
--- a/test/integrity/bld.nix
+++ b/test/integrity/bld.nix
@@ -2,7 +2,7 @@ let
   f = import ../../src/core/importAtom.nix;
   atom = f { } (
     # added to test implicit path conversion when path is a string
-    builtins.toPath ./bld.toml
+    builtins.toPath ./bld.atom
   );
 in
 builtins.deepSeq atom atom
diff --git a/test/pre.toml b/test/pre.atom
similarity index 100%
rename from test/pre.toml
rename to test/pre.atom
diff --git a/test/pre.nix b/test/pre.nix
index 5ceafd6..17b8e70 100644
--- a/test/pre.nix
+++ b/test/pre.nix
@@ -1 +1 @@
-(import ../src/core/importAtom.nix { }) ./pre.toml
+(import ../src/core/importAtom.nix { }) ./pre.atom
diff --git a/test/purity/purity.nix b/test/purity/purity.nix
index 821b3f1..f999f53 100644
--- a/test/purity/purity.nix
+++ b/test/purity/purity.nix
@@ -2,7 +2,7 @@ let
   f = import ../../src/core/importAtom.nix;
   atom = f { __internal__test = true; } (
     # added to test implicit path conversion when path is a string
-    builtins.toPath ./test.toml
+    builtins.toPath ./test.atom
   );
 in
 atom
diff --git a/test/purity/test.toml b/test/purity/test.atom
similarity index 100%
rename from test/purity/test.toml
rename to test/purity/test.atom
diff --git a/test/std-import/default.toml b/test/std-import/default.atom
similarity index 100%
rename from test/std-import/default.toml
rename to test/std-import/default.atom
diff --git a/test/std-import/explicit.toml b/test/std-import/explicit.atom
similarity index 100%
rename from test/std-import/explicit.toml
rename to test/std-import/explicit.atom
diff --git a/test/std-import/import.nix b/test/std-import/import.nix
index 92b83ae..22dd456 100644
--- a/test/std-import/import.nix
+++ b/test/std-import/import.nix
@@ -2,8 +2,8 @@ let
   f = import ../../src/core/importAtom.nix { __internal__test = true; };
 in
 {
-  default = f ./default.toml;
-  noStd = f ./no-std.toml;
-  explicit = f ./explicit.toml;
-  withLib = f ./with-lib.toml;
+  default = f ./default.atom;
+  noStd = f ./no-std.atom;
+  explicit = f ./explicit.atom;
+  withLib = f ./with-lib.atom;
 }
diff --git a/test/std-import/no-std.toml b/test/std-import/no-std.atom
similarity index 100%
rename from test/std-import/no-std.toml
rename to test/std-import/no-std.atom
diff --git a/test/std-import/with-lib.toml b/test/std-import/with-lib.atom
similarity index 100%
rename from test/std-import/with-lib.toml
rename to test/std-import/with-lib.atom