judges requirements

Tasks.md

@@ -38,7 +38,15 @@ Basic information about tasks is on [Assignments overview](https://github.com/Re
 
 Judges are treated as normal external command, so there is no special task for them. All judges are adopted from old Codex with only very small modifications. Judges base directory is in `${JUDGES_DIR}` variable, which can be used in job config file.
 
-TODO: judges requirements by other part of ReCodEx...
+For future extensibility is **critical** that judges have some shared **interface** of calling and return values.
+- Parameters: There are two mandatory positional parameters which has to be files for comparision
+- Results:
+  - _everything OK_
+    - exitcode: 0
+    - stdout: there is one line with double value which should be percentage of similarity of two given files
+  - _error during execution_
+    - exitcode: 1
+    - stderr: there should be description of error
 
 **recodex-judge-normal** is base judge used by most of exercises. This judge compares two text files. It compares only text tokens regardless amount of whitespace between them.
 ```