diff --git a/include/evm.h b/include/evm.h
index eb5864a..84fee65 100644
--- a/include/evm.h
+++ b/include/evm.h
@@ -107,9 +107,27 @@ struct evm_tx_context {
 
 struct evm_context;
 
+/// Get transaction context callback function.
+///
+/// This callback function is used by an EVM to retrieve the transaction and
+/// block context.
+///
+/// @param[out] result   The returned transaction context.
+///                      @see ::evm_tx_context.
+/// @param      context  The pointer to the Host execution context.
+///                      @see ::evm_context.
 typedef void (*evm_get_tx_context_fn)(struct evm_tx_context* result,
                                       struct evm_context* context);
 
+/// Get block hash callback function..
+///
+/// This callback function is used by an EVM to query the block hash of
+/// a given block.
+///
+/// @param[out] result   The returned block hash value.
+/// @param      context  The pointer to the Host execution context.
+/// @param      number   The block number. Must be a value between
+//                       (and including) 0 and 255.
 typedef void (*evm_get_block_hash_fn)(struct evm_uint256be* result,
                                       struct evm_context* context,
                                       int64_t number);