diff --git a/README.md b/README.md
index bef57de..88f7682 100644
--- a/README.md
+++ b/README.md
@@ -2,9 +2,9 @@
 
 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.
+- [ ] Organize variables in each function to the top?
 
 CLI utility for initializing projects in reproducible ways.
 
diff --git a/include/error.h b/include/error.h
index 620d695..f5ce2ea 100644
--- a/include/error.h
+++ b/include/error.h
@@ -12,7 +12,7 @@ enum ErrorCode {
   ERROR_CONFIG_TARGET_INVALID,
   ERROR_CONFIG_TARGET_NOT_DIR,
 
-  ERROR_PARSER_SPEC_JSON_CANNOT_OPEN,
+  ERROR_PARSER_SPEC_JSON_INVALID,
   ERROR_PARSER_SPEC_JSON_INVALID_SYNTAX,
 
   ERROR_VALIDATOR_TOP_LEVEL_NOT_OBJECT,
diff --git a/include/evaluator.h b/include/evaluator.h
index e14c899..809a93f 100644
--- a/include/evaluator.h
+++ b/include/evaluator.h
@@ -2,16 +2,10 @@
 #define _BOOTSTRAP_EVALUATOR_H
 
 #include "config.h"
+#include "error.h"
 #include "validator.h"
 
-enum SpecEvaluationError {
-  // Then `run.sh` file could not be found.
-  SEE_RUN_SH_NOT_FOUND = 1,
-  // The provided input does not match the expected prompt response type.
-  SEE_INVALID_PROMPT_RESPONSE,
-};
-
-enum SpecEvaluationError evaluate_spec_json(
+struct Error *evaluate_spec_json(
   const struct Config *const config, const struct DynArray *const prompts
 );
 
diff --git a/include/parser.h b/include/parser.h
index e1fb4f0..4e5fe12 100644
--- a/include/parser.h
+++ b/include/parser.h
@@ -3,23 +3,15 @@
 
 #include "cJSON.h"
 #include "config.h"
+#include "error.h"
 
-enum SpecParseError {
-  // The `spec.json` file exists but cannot be open.
-  SPE_CANNOT_OPEN = 1,
-  // The JSON of the corresponding file is not syntactically valid.
-  SPE_INVALID_SYNTAX,
-};
-
-/*
+/**
 Reads in the `spec.json` file relative to the paths of the provided @Config.
 
 A spec directory does not necessarily contain a `spec.json` file. If this file
 cannot be found, the @parsed pointer is set to NULL with a success return code.
-
-@return: 0 on success and a @SpecParseError otherwise.
 */
-enum SpecParseError parse_spec_json(
+struct Error *parse_spec_json(
   const struct Config *const config, cJSON **parsed
 );
 
diff --git a/include/validator.h b/include/validator.h
index 61c99d0..05714a6 100644
--- a/include/validator.h
+++ b/include/validator.h
@@ -3,6 +3,7 @@
 
 #include "cJSON.h"
 #include "dyn_array.h"
+#include "error.h"
 
 enum FieldType {
   FT_STRING = 1,
@@ -14,17 +15,7 @@ struct Field {
   const char *prompt;
 };
 
-enum SpecValidationError {
-  // The top-level JSON value of a `spec.json` file must be a JSON object.
-  SVE_TOPLEVEL_NOT_OBJECT = 1,
-  // The field is not a JSON object.
-  SVE_FIELD_NOT_OBJECT,
-  SVE_FIELD_TYPE_INVALID,
-  SVE_FIELD_TYPE_UNKNOWN,
-  SVE_FIELD_PROMPT_INVALID,
-};
-
-enum SpecValidationError validate_spec_json(
+struct Error *validate_spec_json(
   const cJSON *const parsed, struct DynArray **fields
 );
 
diff --git a/main.c b/main.c
index d2ffed9..f7a7cfb 100644
--- a/main.c
+++ b/main.c
@@ -12,6 +12,7 @@
 
 static int run(const char *root_dir, const char *target) {
   int retval = EXIT_FAILURE;
+
   char *cwd = getcwd(0, 0);
   if (!root_dir) {
     root_dir = getenv("BOOTSTRAP_ROOT_DIR");
@@ -26,46 +27,19 @@ static int run(const char *root_dir, const char *target) {
   }
 
   cJSON *parsed = 0;
-  switch (parse_spec_json(config, &parsed)) {
-  case SPE_CANNOT_OPEN:
-    fprintf(stderr, "Cannot open `%s/spec.json`.\n", target);
-    goto cleanup_config;
-  case SPE_INVALID_SYNTAX:
-    fprintf(stderr, "`%s/spec.json` is not valid JSON.\n", target);
+  if ((error = parse_spec_json(config, &parsed))) {
+    fprintf(stderr, "%s", error->message);
     goto cleanup_config;
   }
 
   struct DynArray *prompts = 0;
-  switch (validate_spec_json(parsed, &prompts)) {
-  case SVE_TOPLEVEL_NOT_OBJECT:
-    fprintf(stderr, "`%s/spec.json` is not a JSON object.\n", target);
-    goto cleanup_parsed;
-  case SVE_FIELD_NOT_OBJECT:
-    fprintf(
-      stderr,
-      "Encountered child in `%s/spec.json` that is not a JSON object.\n",
-      target
-    );
-    goto cleanup_parsed;
-  case SVE_FIELD_TYPE_INVALID:
-    fprintf(stderr, "Types must be string values.\n");
-    goto cleanup_parsed;
-  case SVE_FIELD_TYPE_UNKNOWN:
-    fprintf(
-      stderr, "Encountered an unknown `type` in `%s/spec.json`.\n", target
-    );
-    goto cleanup_parsed;
-  case SVE_FIELD_PROMPT_INVALID:
-    fprintf(stderr, "Prompts must be string values.\n");
+  if ((error = validate_spec_json(parsed, &prompts))) {
+    fprintf(stderr, "%s", error->message);
     goto cleanup_parsed;
   }
 
-  switch (evaluate_spec_json(config, prompts)) {
-  case SEE_RUN_SH_NOT_FOUND:
-    fprintf(stderr, "Could not find `%s/run.sh`.\n", target);
-    goto cleanup_parsed;
-  case SEE_INVALID_PROMPT_RESPONSE:
-    fprintf(stderr, "Could not interpret response.\n");
+  if ((error = evaluate_spec_json(config, prompts))) {
+    fprintf(stderr, "%s", error->message);
     goto cleanup_parsed;
   }
 
diff --git a/src/evaluator.c b/src/evaluator.c
index 328e7db..11dbbd5 100644
--- a/src/evaluator.c
+++ b/src/evaluator.c
@@ -7,7 +7,7 @@
 #include "path.h"
 #include "string_buf.h"
 
-static enum SpecEvaluationError find_run_sh(const struct Config *const config) {
+static struct Error *find_run_sh(const struct Config *const config) {
   struct stat sb;
   const char *segments[] = {config->root_dir, config->target, "run.sh"};
   char *filepath =
@@ -16,18 +16,25 @@ static enum SpecEvaluationError find_run_sh(const struct Config *const config) {
   free(filepath);
 
   if (stat_res == -1 && errno == ENOENT) {
-    return SEE_RUN_SH_NOT_FOUND;
+    return ERROR_NEW(
+      ERROR_EVALUATOR_RUN_SH_NOT_FOUND,
+      "Could not find ",
+      config->target,
+      "/run.sh"
+    );
   }
 
+  // TODO: Check run.sh is executable.
+
   return 0;
 }
 
-enum SpecEvaluationError evaluate_spec_json(
+struct Error *evaluate_spec_json(
   const struct Config *const config, const struct DynArray *const prompts
 ) {
-  enum SpecEvaluationError retval = find_run_sh(config);
-  if (retval != 0) {
-    return retval;
+  struct Error *error = find_run_sh(config);
+  if (error) {
+    return error;
   }
 
   if (prompts) {
@@ -56,7 +63,6 @@ enum SpecEvaluationError evaluate_spec_json(
 
   // TODO: Want to return this status out.
   int status = system(command);
-  ;
 
   return 0;
 }
diff --git a/src/parser.c b/src/parser.c
index 7254bb0..8443005 100644
--- a/src/parser.c
+++ b/src/parser.c
@@ -7,31 +7,35 @@
 
 #include "path.h"
 
-static int find_spec_json(const struct Config *const config, FILE **handle) {
+static struct Error *find_spec_json(
+  const struct Config *const config, FILE **handle
+) {
   const char *segments[] = {config->root_dir, config->target, "spec.json"};
   char *filepath =
     join_path_segments(sizeof(segments) / sizeof(char *), segments);
 
-  int retval = 0;
+  struct Error *error = 0;
   // It is ok if the file does not exist. It is not ok if we couldn't open the
   // file for any other reason.
   *handle = fopen(filepath, "r");
   if (!*handle && errno != ENOENT) {
-    retval = errno;
+    error = ERROR_NEW(
+      ERROR_PARSER_SPEC_JSON_INVALID, config->target, "/spec.json is invalid."
+    );
   }
 
   free(filepath);
-  return retval;
+  return error;
 }
 
-enum SpecParseError parse_spec_json(
+struct Error *parse_spec_json(
   const struct Config *const config, cJSON **parsed
 ) {
   FILE *handle = 0;
-  int retval = find_spec_json(config, &handle);
+  struct Error *error = find_spec_json(config, &handle);
 
-  if (retval != 0) {
-    return SPE_CANNOT_OPEN;
+  if (error) {
+    return error;
   }
 
   // The `spec.json` file does not exist.
@@ -55,7 +59,10 @@ enum SpecParseError parse_spec_json(
 
   // Can use `cJSON_GetErrorPtr()` to get the actual error message.
   if (!*parsed) {
-    return SPE_INVALID_SYNTAX;
+    return ERROR_NEW(
+      ERROR_PARSER_SPEC_JSON_INVALID_SYNTAX,
+      "The spec.json file contains invalid JSON."
+    );
   }
 
   return 0;
diff --git a/src/validator.c b/src/validator.c
index 5c48f36..9093339 100644
--- a/src/validator.c
+++ b/src/validator.c
@@ -2,27 +2,39 @@
 
 #include <string.h>
 
-static enum SpecValidationError read_field(
-  const cJSON *const field, struct Field **out
-) {
+static struct Error *read_field(const cJSON *const field, struct Field **out) {
   if (!cJSON_IsObject(field)) {
-    return SVE_FIELD_NOT_OBJECT;
+    return ERROR_NEW(
+      ERROR_VALIDATOR_FIELD_NOT_OBJECT,
+      "Field \"",
+      field->string,
+      "\" is not a JSON object."
+    );
   }
 
-  enum SpecValidationError retval = 0;
-
+  struct Error *error = 0;
   *out = malloc(sizeof(struct Field));
 
   const cJSON *type = cJSON_GetObjectItemCaseSensitive(field, "type");
   if (!cJSON_IsString(type)) {
-    retval = SVE_FIELD_TYPE_INVALID;
+    error = ERROR_NEW(
+      ERROR_VALIDATOR_FIELD_TYPE_INVALID,
+      "Field \"",
+      field->string,
+      "\" has non-string \"type\"."
+    );
     goto cleanup;
   }
 
   if (strcmp(type->valuestring, "STRING") == 0) {
     (*out)->type = FT_STRING;
   } else {
-    retval = SVE_FIELD_TYPE_UNKNOWN;
+    error = ERROR_NEW(
+      ERROR_VALIDATOR_FIELD_TYPE_UNKNOWN,
+      "Field \"",
+      field->string,
+      "\" has unknown \"type\"."
+    );
     goto cleanup;
   }
 
@@ -30,18 +42,23 @@ static enum SpecValidationError read_field(
   if (cJSON_IsString(prompt)) {
     (*out)->prompt = prompt->valuestring;
   } else {
-    retval = SVE_FIELD_PROMPT_INVALID;
+    error = ERROR_NEW(
+      ERROR_VALIDATOR_FIELD_PROMPT_INVALID,
+      "Field \"",
+      field->string,
+      "\" has non-string \"prompt\"."
+    );
     goto cleanup;
   }
 
-  return retval;
+  return error;
 
 cleanup:
   free(*out);
-  return retval;
+  return error;
 }
 
-enum SpecValidationError validate_spec_json(
+struct Error *validate_spec_json(
   const cJSON *const parsed, struct DynArray **fields
 ) {
   *fields = 0;
@@ -52,10 +69,13 @@ enum SpecValidationError validate_spec_json(
   }
 
   if (!cJSON_IsObject(parsed)) {
-    return SVE_TOPLEVEL_NOT_OBJECT;
+    return ERROR_NEW(
+      ERROR_VALIDATOR_TOP_LEVEL_NOT_OBJECT,
+      "Top-level JSON value in spec.json is not an object."
+    );
   }
 
-  enum SpecValidationError retval = 0;
+  struct Error *error = 0;
   // `cJSON_GetArraySize` works because internally JSON objects are stored as
   // arrays.
   *fields = dyn_array_new(cJSON_GetArraySize(parsed));
@@ -63,8 +83,8 @@ enum SpecValidationError validate_spec_json(
   cJSON *child = parsed->child;
   while (child) {
     struct Field *field = 0;
-    retval = read_field(child, &field);
-    if (retval) {
+    error = read_field(child, &field);
+    if (error) {
       goto cleanup;
     }
     dyn_array_push(*fields, field);
@@ -78,5 +98,5 @@ cleanup:
     dyn_array_free(*fields);
     *fields = 0;
   }
-  return retval;
+  return error;
 }
diff --git a/test/test_parser.h b/test/test_parser.h
index 676b32f..ad1033e 100644
--- a/test/test_parser.h
+++ b/test/test_parser.h
@@ -49,8 +49,8 @@ static void test_parser_missing() {
   struct TestParserFixture *fixture = test_parser_setup("no_spec_json");
 
   cJSON *parsed = 0;
-  enum SpecParseError retval = parse_spec_json(&fixture->config, &parsed);
-  sput_fail_unless(retval == 0, "no spec.json, success");
+  struct Error *error = parse_spec_json(&fixture->config, &parsed);
+  sput_fail_unless(error == 0, "no spec.json, success");
   sput_fail_unless(parsed == 0, "no spec.json, no parsed");
 
   test_parser_teardown(fixture);
@@ -60,8 +60,8 @@ static void test_parser_minimal() {
   struct TestParserFixture *fixture = test_parser_setup("minimal_spec_json");
 
   cJSON *parsed = 0;
-  enum SpecParseError retval = parse_spec_json(&fixture->config, &parsed);
-  sput_fail_unless(retval == 0, "minimal spec.json, success");
+  struct Error *error = parse_spec_json(&fixture->config, &parsed);
+  sput_fail_unless(error == 0, "minimal spec.json, success");
   sput_fail_unless(parsed != 0, "minimal spec.json, parsed");
 
   test_parser_teardown(fixture);
@@ -71,10 +71,12 @@ static void test_parser_invalid() {
   struct TestParserFixture *fixture = test_parser_setup("invalid_spec_json");
 
   cJSON *parsed = 0;
-  enum SpecParseError retval = parse_spec_json(&fixture->config, &parsed);
+  struct Error *error = parse_spec_json(&fixture->config, &parsed);
   sput_fail_unless(
-    retval == SPE_INVALID_SYNTAX, "invalid spec.json, INVALID_SYNTAX"
+    error->code == ERROR_PARSER_SPEC_JSON_INVALID_SYNTAX,
+    "invalid spec.json, INVALID_SYNTAX"
   );
+  error_free(error);
   sput_fail_unless(parsed == 0, "invalid spec.json, not parsed");
 
   test_parser_teardown(fixture);
diff --git a/test/test_validator.h b/test/test_validator.h
index 4fb5bc4..1de69ed 100644
--- a/test/test_validator.h
+++ b/test/test_validator.h
@@ -30,9 +30,11 @@ static void test_validator_teardown(struct TestValidatorFixture *fixture) {
 static void test_validator_toplevel_not_object() {
   struct TestValidatorFixture *fixture = test_validator_setup("[]");
 
-  enum SpecValidationError retval =
-    validate_spec_json(fixture->parsed, &fixture->prompts);
-  sput_fail_unless(retval == SVE_TOPLEVEL_NOT_OBJECT, "top-level not object");
+  struct Error *error = validate_spec_json(fixture->parsed, &fixture->prompts);
+  sput_fail_unless(
+    error->code == ERROR_VALIDATOR_TOP_LEVEL_NOT_OBJECT, "top-level not object"
+  );
+  error_free(error);
 
   test_validator_teardown(fixture);
 }
@@ -41,9 +43,11 @@ static void test_validator_field_not_object() {
   struct TestValidatorFixture *fixture =
     test_validator_setup("{\"key\": \"$UNKNOWN\"}");
 
-  enum SpecValidationError retval =
-    validate_spec_json(fixture->parsed, &fixture->prompts);
-  sput_fail_unless(retval == SVE_FIELD_NOT_OBJECT, "field not object");
+  struct Error *error = validate_spec_json(fixture->parsed, &fixture->prompts);
+  sput_fail_unless(
+    error->code == ERROR_VALIDATOR_FIELD_NOT_OBJECT, "field not object"
+  );
+  error_free(error);
 
   test_validator_teardown(fixture);
 }
@@ -57,9 +61,11 @@ static void test_validator_field_type_invalid() {
     "}"
   );
 
-  enum SpecValidationError retval =
-    validate_spec_json(fixture->parsed, &fixture->prompts);
-  sput_fail_unless(retval == SVE_FIELD_TYPE_INVALID, "field type invalid");
+  struct Error *error = validate_spec_json(fixture->parsed, &fixture->prompts);
+  sput_fail_unless(
+    error->code == ERROR_VALIDATOR_FIELD_TYPE_INVALID, "field type invalid"
+  );
+  error_free(error);
 
   test_validator_teardown(fixture);
 }
@@ -73,9 +79,11 @@ static void test_validator_field_type_unknown() {
     "}"
   );
 
-  enum SpecValidationError retval =
-    validate_spec_json(fixture->parsed, &fixture->prompts);
-  sput_fail_unless(retval == SVE_FIELD_TYPE_UNKNOWN, "field type unknown");
+  struct Error *error = validate_spec_json(fixture->parsed, &fixture->prompts);
+  sput_fail_unless(
+    error->code == ERROR_VALIDATOR_FIELD_TYPE_UNKNOWN, "field type unknown"
+  );
+  error_free(error);
 
   test_validator_teardown(fixture);
 }
@@ -90,9 +98,11 @@ static void test_validator_field_prompt_invalid() {
     "}"
   );
 
-  enum SpecValidationError retval =
-    validate_spec_json(fixture->parsed, &fixture->prompts);
-  sput_fail_unless(retval == SVE_FIELD_PROMPT_INVALID, "field prompt invalid");
+  struct Error *error = validate_spec_json(fixture->parsed, &fixture->prompts);
+  sput_fail_unless(
+    error->code == ERROR_VALIDATOR_FIELD_PROMPT_INVALID, "field prompt invalid"
+  );
+  error_free(error);
 
   test_validator_teardown(fixture);
 }
@@ -107,9 +117,8 @@ static void test_validator_valid() {
     "}"
   );
 
-  enum SpecValidationError retval =
-    validate_spec_json(fixture->parsed, &fixture->prompts);
-  sput_fail_unless(retval == 0, "valid");
+  struct Error *error = validate_spec_json(fixture->parsed, &fixture->prompts);
+  sput_fail_unless(error == 0, "valid");
 
   test_validator_teardown(fixture);
 }