diff --git a/README.md b/README.md
index 4b1a13d..bef57de 100644
--- a/README.md
+++ b/README.md
@@ -1,5 +1,11 @@
 # bootstrap
 
+TODO:
+- [ ] Make free-ing data consistent with null pointers.
+- [ ] Make error handling consistent.
+- [ ] Add documentation throughout (ownership, docstrings, etc.).
+- [ ] Have main.c return status code of run.sh.
+
 CLI utility for initializing projects in reproducible ways.
 
 ## Overview
diff --git a/include/config.h b/include/config.h
index 7e6b21b..d02fca5 100644
--- a/include/config.h
+++ b/include/config.h
@@ -1,6 +1,8 @@
 #ifndef _BOOTSTRAP_CONFIG_H
 #define _BOOTSTRAP_CONFIG_H
 
+#include "error.h"
+
 struct Config {
   // The directory the `bootstrap` command was run from.
   // OWNERSHIP: Does not own this pointer.
@@ -13,20 +15,7 @@ struct Config {
   const char *target;
 };
 
-enum ConfigError {
-  // The $CWD could not be retrieved.
-  CE_ENV_CWD_INVALID = 1,
-  // The $BOOTSTRAP_ROOT_DIR environment variable is empty.
-  CE_ENV_ROOT_DIR_INVALID,
-  // The target argument is invalid.
-  CE_TARGET_INVALID,
-  // No spec with the given name was found.
-  CE_TARGET_NOT_FOUND,
-  // The spec is not a directory.
-  CE_TARGET_NOT_DIR,
-};
-
-enum ConfigError config_load(
+struct Error *config_load(
   const char *cwd,
   const char *root_dir,
   const char *target,
diff --git a/include/error.h b/include/error.h
index 2b4fdac..620d695 100644
--- a/include/error.h
+++ b/include/error.h
@@ -1,12 +1,15 @@
 #ifndef _BOOTSTRAP_ERROR_H
 #define _BOOTSTRAP_ERROR_H
 
-enum ErrorCode {
-  SUCCESS = 0,
+#include <stdlib.h>
 
-  ERROR_CONFIG_ENV_CWD_INVALID,
+#include "string_buf.h"
+
+enum ErrorCode {
+  ERROR_CONFIG_ENV_CWD_INVALID = 1,
   ERROR_CONFIG_ENV_ROOT_DIR_INVALID,
   ERROR_CONFIG_TARGET_NOT_FOUND,
+  ERROR_CONFIG_TARGET_INVALID,
   ERROR_CONFIG_TARGET_NOT_DIR,
 
   ERROR_PARSER_SPEC_JSON_CANNOT_OPEN,
@@ -27,4 +30,55 @@ struct Error {
   const char *message;
 };
 
+static inline struct Error *priv_error_new(
+  enum ErrorCode code, size_t n, const char *messages[static n]
+) {
+  struct Error *e = malloc(sizeof(struct Error));
+  e->code = code;
+  struct StringBuf *sb = string_buf_new(1024);
+  for (int i = 0; i < n; ++i) {
+    string_buf_sappend(sb, messages[i]);
+  }
+  e->message = string_buf_convert(sb);
+  return e;
+}
+
+// clang-format off
+
+/**
+Return the number of elements of `__VA_ARGS__`.
+
+Take the `__VA_ARGS__` list and append a list of decreasing numbers
+31, 30, ..., 0. Then, by using ALEN0, return the 31st element of that list.
+*/
+#define ALEN(...) \
+  ALEN0(          \
+    __VA_ARGS__,  \
+    0x1F, 0x1E, 0x1D, 0x1C, 0x1B, 0x1A, 0x19, 0x18, \
+    0x17, 0x16, 0x15, 0x14, 0x13, 0x12, 0x11, 0x10, \
+    0x0E, 0x0F, 0x0D, 0x0C, 0x0B, 0x0A, 0x09, 0x08, \
+    0x07, 0x06, 0x05, 0x04, 0x03, 0x02, 0x01, 0x00)
+
+#define ALEN0( \
+  _00, _01, _02, _03, _04, _05, _06, _07, \
+  _08, _09, _0A, _0B, _0C, _0D, _0F, _0E, \
+  _10, _11, _12, _13, _14, _15, _16, _17, \
+  _18, _19, _1A, _1B, _1C, _1D, _1E, _1F, \
+  ...) _1F
+
+/**
+Create a new `struct Error` instance.
+*/
+#define ERROR_NEW(code, ...) \
+  ERROR_NEW0(code, ALEN(__VA_ARGS__), __VA_ARGS__)
+
+#define ERROR_NEW0(code, nargs, ...)                                   \
+  priv_error_new(                                                      \
+    (code), (nargs + 1), (const char * [nargs + 1]){__VA_ARGS__, "\n"} \
+  )
+
+// clang-format on
+
+void error_free(struct Error *error);
+
 #endif /* _BOOTSTRAP_ERROR_H */
diff --git a/include/string_buf.h b/include/string_buf.h
index 224270b..7f9336f 100644
--- a/include/string_buf.h
+++ b/include/string_buf.h
@@ -9,7 +9,13 @@
  * A `char*` wrapper. Appending `char`s or NUL-terminated strings allocates
  * additional space as needed.
  */
-struct StringBuf;
+struct StringBuf {
+  char *buf;
+  // The length of @buf excluding `NUL`.
+  size_t size;
+  // The allocated size of @buf including `NUL`.
+  size_t _capacity;
+};
 
 /**
  * Create a new `StringBuf` instance.
diff --git a/main.c b/main.c
index eb50289..d2ffed9 100644
--- a/main.c
+++ b/main.c
@@ -5,6 +5,7 @@
 
 #include "cJSON.h"
 #include "config.h"
+#include "error.h"
 #include "evaluator.h"
 #include "parser.h"
 #include "validator.h"
@@ -16,26 +17,11 @@ static int run(const char *root_dir, const char *target) {
     root_dir = getenv("BOOTSTRAP_ROOT_DIR");
   }
 
+  struct Error *error = 0;
   struct Config *config = 0;
-  switch (config_load(cwd, root_dir, target, &config)) {
-  case CE_ENV_CWD_INVALID:
-    fprintf(stderr, "Could not retrieve $CWD.\n");
-    goto cleanup_cwd;
-  case CE_ENV_ROOT_DIR_INVALID:
-    fprintf(
-      stderr,
-      "Either supply a value to `-d` or specify the $BOOTSTRAP_ROOT_DIR "
-      "environment variable.\n"
-    );
-    goto cleanup_cwd;
-  case CE_TARGET_INVALID:
-    fprintf(stderr, "Spec `%s` is invalid.\n", target);
-    goto cleanup_cwd;
-  case CE_TARGET_NOT_FOUND:
-    fprintf(stderr, "Spec `%s` not found.\n", target);
-    goto cleanup_cwd;
-  case CE_TARGET_NOT_DIR:
-    fprintf(stderr, "Spec `%s` is not a directory.\n", target);
+
+  if ((error = config_load(cwd, root_dir, target, &config))) {
+    fprintf(stderr, "%s", error->message);
     goto cleanup_cwd;
   }
 
@@ -100,6 +86,7 @@ cleanup_config:
 
 cleanup_cwd:
   free(cwd);
+  error_free(error);
   return retval;
 }
 
diff --git a/specs/clang/run.sh b/specs/clang/run.sh
deleted file mode 100755
index ea3761b..0000000
--- a/specs/clang/run.sh
+++ /dev/null
@@ -1,3 +0,0 @@
-#!/usr/bin/env bash
-
-cp -r template/* "$OUT"
diff --git a/specs/clang/template/flake.nix b/specs/clang/template/flake.nix
deleted file mode 100644
index 8d05f24..0000000
--- a/specs/clang/template/flake.nix
+++ /dev/null
@@ -1,35 +0,0 @@
-{
-  description = ''
-    An opinionated clang flake.
-  '';
-
-  inputs = {
-    flake-utils.url = "github:numtide/flake-utils";
-    nixpkgs.url = "github:nixos/nixpkgs/nixos-unstable";
-  };
-
-  outputs = { self, nixpkgs, flake-utils }:
-    flake-utils.lib.eachDefaultSystem (system:
-      let
-        pkgs = nixpkgs.legacyPackages.${system};
-
-        codelldb = pkgs.writeShellScriptBin "codelldb" ''
-          exec ${pkgs.vscode-extensions.vadimcn.vscode-lldb}/share/vscode/extensions/vadimcn.vscode-lldb/adapter/codelldb "$@"
-        '';
-      in
-      {
-        devShells.default = pkgs.mkShell.override {
-          # https://nixos.wiki/wiki/Using_Clang_instead_of_GCC
-          stdenv = pkgs.clangStdenv;
-        } {
-          packages = with pkgs; [
-            bear
-            clang-tools
-            codelldb
-          ];
-          buildInputs = with pkgs; [
-            ncurses
-          ];
-        };
-      });
-}
diff --git a/specs/clang/template/main.c b/specs/clang/template/main.c
deleted file mode 100644
index 7cbc9bc..0000000
--- a/specs/clang/template/main.c
+++ /dev/null
@@ -1,3 +0,0 @@
-#include <stdlib.h>
-
-int main(int argc, char **argv) { return EXIT_SUCCESS; }
diff --git a/specs/clang/template/.envrc b/specs/test/run.sh
old mode 100644
new mode 100755
similarity index 52%
rename from specs/clang/template/.envrc
rename to specs/test/run.sh
index b9238c3..c914ca6
--- a/specs/clang/template/.envrc
+++ b/specs/test/run.sh
@@ -1,3 +1,3 @@
 #!/usr/bin/env bash
 
-use flake
+echo "hello world"
diff --git a/src/config.c b/src/config.c
index 34b177b..1d4df64 100644
--- a/src/config.c
+++ b/src/config.c
@@ -1,5 +1,6 @@
 #include "config.h"
 
+#include <assert.h>
 #include <errno.h>
 #include <stdlib.h>
 #include <string.h>
@@ -7,41 +8,48 @@
 
 #include "path.h"
 
-enum ConfigError config_load(
+struct Error *config_load(
   const char *cwd,
   const char *root_dir,
   const char *target,
   struct Config **config
 ) {
   if (cwd == 0) {
-    return CE_ENV_CWD_INVALID;
+    return ERROR_NEW(ERROR_CONFIG_ENV_CWD_INVALID, "Could not retrieve $CWD.");
   }
   if (root_dir == 0) {
-    return CE_ENV_ROOT_DIR_INVALID;
+    return ERROR_NEW(
+      ERROR_CONFIG_ENV_ROOT_DIR_INVALID, "No specified root directory."
+    );
   }
-  if (target == 0) {
-    return CE_TARGET_INVALID;
+  assert(target);
+
+  // Check if the specified directory exists.
+  const char *segments[] = {root_dir, target};
+  char *filepath =
+    join_path_segments(sizeof(segments) / sizeof(char *), segments);
+
+  struct stat sb;
+  int stat_res = stat(filepath, &sb);
+  struct Error *error = 0;
+
+  if (stat_res == -1) {
+    if (errno == ENOENT) {
+      error = ERROR_NEW(
+        ERROR_CONFIG_TARGET_NOT_FOUND, "Spec ", filepath, " not found."
+      );
+    } else {
+      error = ERROR_NEW(
+        ERROR_CONFIG_TARGET_INVALID, "Spec ", filepath, " is invalid."
+      );
+    }
+    goto cleanup;
   }
-
-  {  // Check if the specified directory exists.
-    struct stat sb;
-
-    const char *segments[] = {root_dir, target};
-    char *filepath =
-      join_path_segments(sizeof(segments) / sizeof(char *), segments);
-
-    int stat_res = stat(filepath, &sb);
-    free(filepath);
-
-    if (stat_res == -1) {
-      if (errno == ENOENT) {
-        return CE_TARGET_NOT_FOUND;
-      }
-      return CE_TARGET_INVALID;
-    }
-    if (!S_ISDIR(sb.st_mode)) {
-      return CE_TARGET_NOT_DIR;
-    }
+  if (!S_ISDIR(sb.st_mode)) {
+    error = ERROR_NEW(
+      ERROR_CONFIG_TARGET_NOT_DIR, "Spec ", filepath, " is not a directory."
+    );
+    goto cleanup;
   }
 
   *config = malloc(sizeof(struct Config));
@@ -49,7 +57,9 @@ enum ConfigError config_load(
   (*config)->root_dir = root_dir;
   (*config)->target = target;
 
-  return 0;
+cleanup:
+  free(filepath);
+  return error;
 }
 
 void config_free(struct Config *config) {
diff --git a/src/error.c b/src/error.c
new file mode 100644
index 0000000..7ed0cb0
--- /dev/null
+++ b/src/error.c
@@ -0,0 +1,10 @@
+#include "error.h"
+
+void error_free(struct Error *error) {
+  if (!error) {
+    return;
+  }
+  free((void *)error->message);
+  free(error);
+  error = 0;
+}
diff --git a/src/string_buf.c b/src/string_buf.c
index fdb98e7..cc2c7ce 100644
--- a/src/string_buf.c
+++ b/src/string_buf.c
@@ -5,14 +5,6 @@
 #include <stdlib.h>
 #include <string.h>
 
-struct StringBuf {
-  char *buf;
-  // The length of @buf excluding `NUL`.
-  size_t size;
-  // The allocated size of @buf including `NUL`.
-  size_t _capacity;
-};
-
 struct StringBuf *string_buf_new(size_t capacity) {
   struct StringBuf *sb = malloc(sizeof(struct StringBuf));
   sb->buf = calloc(capacity, sizeof(char));
@@ -27,12 +19,6 @@ size_t string_buf_size(struct StringBuf *sb) {
   return sb->size;
 }
 
-const char *string_buf_value(struct StringBuf *sb) {
-  assert(sb);
-
-  return sb->buf;
-}
-
 void string_buf_cappend(struct StringBuf *sb, char c) {
   assert(sb);
 
diff --git a/test/test_config.h b/test/test_config.h
index 6512a72..722fa71 100644
--- a/test/test_config.h
+++ b/test/test_config.h
@@ -36,15 +36,17 @@ static void test_config_teardown(struct TestConfigFixture *fixture) {
 static void test_config_load_invalid_args() {
   struct TestConfigFixture *fixture = test_config_setup();
 
+  struct Error *error = 0;
   struct Config *config = 0;
-  enum ConfigError retval = 0;
 
-  retval = config_load(0, fixture->root_dir, fixture->target, &config);
-  sput_fail_unless(retval == CE_ENV_CWD_INVALID, "target == 0");
-  retval = config_load(fixture->cwd, 0, fixture->target, &config);
-  sput_fail_unless(retval == CE_ENV_ROOT_DIR_INVALID, "root_dir == 0");
-  retval = config_load(fixture->cwd, fixture->root_dir, 0, &config);
-  sput_fail_unless(retval == CE_TARGET_INVALID, "target == 0");
+  error = config_load(0, fixture->root_dir, fixture->target, &config);
+  sput_fail_unless(error->code == ERROR_CONFIG_ENV_CWD_INVALID, "cwd == 0");
+  error_free(error);
+  error = config_load(fixture->cwd, 0, fixture->target, &config);
+  sput_fail_unless(
+    error->code == ERROR_CONFIG_ENV_ROOT_DIR_INVALID, "root_dir == 0"
+  );
+  error_free(error);
 
   test_config_teardown(fixture);
 }
@@ -52,10 +54,14 @@ static void test_config_load_invalid_args() {
 static void test_config_load_spec_not_found() {
   struct TestConfigFixture *fixture = test_config_setup();
 
+  struct Error *error = 0;
   struct Config *config = 0;
-  enum ConfigError retval =
-    config_load(fixture->cwd, fixture->root_dir, "not_found", &config);
-  sput_fail_unless(retval == CE_TARGET_NOT_FOUND, "target not found");
+
+  error = config_load(fixture->cwd, fixture->root_dir, "not_found", &config);
+  sput_fail_unless(
+    error->code == ERROR_CONFIG_TARGET_NOT_FOUND, "target not found"
+  );
+  error_free(error);
 
   test_config_teardown(fixture);
 }
@@ -63,10 +69,14 @@ static void test_config_load_spec_not_found() {
 static void test_config_load_spec_not_dir() {
   struct TestConfigFixture *fixture = test_config_setup();
 
+  struct Error *error = 0;
   struct Config *config = 0;
-  enum ConfigError retval =
-    config_load(fixture->cwd, fixture->root_dir, "not_dir", &config);
-  sput_fail_unless(retval == CE_TARGET_NOT_DIR, "target not dir");
+
+  error = config_load(fixture->cwd, fixture->root_dir, "not_dir", &config);
+  sput_fail_unless(
+    error->code == ERROR_CONFIG_TARGET_NOT_DIR, "target not dir"
+  );
+  error_free(error);
 
   test_config_teardown(fixture);
 }
@@ -74,11 +84,12 @@ static void test_config_load_spec_not_dir() {
 static void test_config_load_success() {
   struct TestConfigFixture *fixture = test_config_setup();
 
+  struct Error *error = 0;
   struct Config *config = 0;
-  enum ConfigError retval =
-    config_load(fixture->cwd, fixture->root_dir, fixture->target, &config);
 
-  sput_fail_unless(retval == 0, "config_load() success");
+  error =
+    config_load(fixture->cwd, fixture->root_dir, fixture->target, &config);
+  sput_fail_unless(error == 0, "config_load() success");
   sput_fail_unless(strcmp(config->cwd, fixture->cwd) == 0, "config_load() cwd");
   sput_fail_unless(
     strcmp(config->root_dir, fixture->root_dir) == 0, "config_load() root_dir"