diff --git a/ethcore/src/json_tests/executive.rs b/ethcore/src/json_tests/executive.rs
index 25535adab..11288ae2d 100644
--- a/ethcore/src/json_tests/executive.rs
+++ b/ethcore/src/json_tests/executive.rs
@@ -240,6 +240,7 @@ where
     }
 }
 
+/// run an json executive test
 pub fn json_executive_test<H: FnMut(&str, HookType)>(
     path: &Path,
     json_data: &[u8],
diff --git a/ethcore/src/json_tests/mod.rs b/ethcore/src/json_tests/mod.rs
index 5f1cad9ad..004d86d69 100644
--- a/ethcore/src/json_tests/mod.rs
+++ b/ethcore/src/json_tests/mod.rs
@@ -19,12 +19,14 @@
 mod chain;
 mod difficulty;
 mod executive;
-pub mod runner;
 mod state;
 mod test_common;
 mod transaction;
 mod trie;
 
+/// executor of ethereum/json tests
+pub mod runner;
+
 pub use self::{
     executive::json_executive_test,
     test_common::{debug_include_test, find_json_files_recursive, HookType},
diff --git a/ethcore/src/json_tests/runner.rs b/ethcore/src/json_tests/runner.rs
index 18bad4a7f..4b22146fa 100644
--- a/ethcore/src/json_tests/runner.rs
+++ b/ethcore/src/json_tests/runner.rs
@@ -59,6 +59,7 @@ impl std::ops::AddAssign for TestResult {
     }
 }
 
+/// An executor of ethereum/json tests
 pub struct TestRunner(EthereumTestSuite);
 
 impl TestRunner {
diff --git a/ethcore/src/json_tests/test_common.rs b/ethcore/src/json_tests/test_common.rs
index 2af7616fb..73a6a500c 100644
--- a/ethcore/src/json_tests/test_common.rs
+++ b/ethcore/src/json_tests/test_common.rs
@@ -27,6 +27,7 @@ pub enum HookType {
     OnStop,
 }
 
+/// find all json files recursively from a path
 pub fn find_json_files_recursive(path: &PathBuf) -> Vec<PathBuf> {
     WalkDir::new(path)
         .into_iter()
@@ -36,6 +37,7 @@ pub fn find_json_files_recursive(path: &PathBuf) -> Vec<PathBuf> {
         .collect::<Vec<PathBuf>>()
 }
 
+/// check if the test is selected to execute via TEST_DEBUG environment variable
 pub fn debug_include_test(name: &str) -> bool {
     match std::env::var_os("TEST_DEBUG") {
         Some(s) => s.to_string_lossy().split_terminator(",").any(|expr| {