diff --git a/tests/functional/repl_characterization/README.md b/tests/functional/repl_characterization/README.md
deleted file mode 100644
index 51180618d..000000000
--- a/tests/functional/repl_characterization/README.md
+++ /dev/null
@@ -1,82 +0,0 @@
-# repl characterization tests
-
-> or, literate programming for your REPL tests!
-
-The core idea behind repl-characterization is to make it very easy to write and maintain REPL tests by turning session transcripts directly into tests.
-
-This infrastructure is written in C++ but we want to [rewrite it in functional2][riif2] in the near future.
-
-[riif2]: https://git.lix.systems/lix-project/lix/issues/1196
-
-To write a repl-characterization test, you can open up `nix repl` and then you copy paste the output into the test file, then indent it.
-Add your unindented commentary alongside the output text.
-Add any necessary args.
-Then it should run!
-
-## Syntax
-
-The syntax of repl-characterization contains four types of things:
-- Prompts to the repl, indented: `  nix-repl> 2 + 2` for example.
-- Blocks of output, indented.
-  These are denoted by indented non-empty lines, perhaps with some blank lines between them which are part of the output.
-- Directives, unindented.
-  These are:
-  - `@args some args with "shell quoting"`.
-    Adds the args to the invocation of `nix repl`.
-    Multiple may be used.
-
-    `${PWD}` will be replaced by the actual working directory.
-  - `@should-start false`
-    This is used to indicate that the repl is expected to fail to start, giving some output and no prompt to the system.
-- Commentary.
-  This is any unindented text, including blank lines outside output blocks.
-
-One of the core ideas of the syntax is that it's possible to write an unparser for it such that we can update test session files in-place, retaining your commentary.
-This is [not implemented in the C++ version][bug-autoupdate], and I think we will probably only do it in the Python version.
-
-[bug-autoupdate]: https://git.lix.systems/lix-project/lix/issues/36
-
-Here is a simplified version of the syntax in pseudo-[EBNF]:
-
-[EBNF]: https://en.wikipedia.org/wiki/Extended_Backus%E2%80%93Naur_form
-
-```ebnf
-indent = "  " (* space times config.indent; 2 in practice *) ;
-line-char = ( ? anything but nl ? )+ ;
-nl = "\n" ;
-
-prompt = "nix-repl>" ;
-command = line-char* ;
-prompt-line = indent , prompt , command ;
-
-bool = "true" | "false" ;
-
-args-directive = "args " , line-char+ ;
-should-start-directive = "should-start " , bool ;
-unknown-directive = ? this is an error ? ; (* there's a bug in the C++ impl where we don't actually error on this *)
-directive = args-directive | should-start-directive | unknown-directive ;
-directive-line = "@" , directive ;
-
-(* anything unindented is a comment *)
-commentary-line = line-char+ ;
-
-output-line = indent , line-char+ ;
-output-continuation = output-line? , nl ;
-(* in other words: output blocks are considered to contain any *inner* blank
-   lines within them, but *not* trailing blank lines. This enables updating
-   them automatically while retaining the blank lines surrounding your stanzas
-   in your session.
-
-   This is implemented as a postprocessing step so that our parsing doesn't
-   require lookahead. *)
-output-block = output-line , nl , ((blank-line , nl)+ , output-line , nl)+ ;
-
-input = ((prompt-line | directive-line | commentary-line) , nl) | output-block ;
-file = input* ;
-```
-
-## Usage
-
-Tests are written in `./data/*.test`, and have a corresponding macro call in `./repl_characterization.cc` (the macro thing is basically a hack because the infra was never quite finished).
-
-You can run the suite with `just install && just test --suite installcheck repl-characterization-tests`.
diff --git a/tests/unit/libutil-support/tests/cli-literate-parser.hh b/tests/unit/libutil-support/tests/cli-literate-parser.hh
index 79104689a..55ea5eb81 100644
--- a/tests/unit/libutil-support/tests/cli-literate-parser.hh
+++ b/tests/unit/libutil-support/tests/cli-literate-parser.hh
@@ -2,7 +2,10 @@
 ///@file
 
 #include "lix/libutil/error.hh"
+#include <compare>
+#include <memory>
 #include <optional>
+#include <sstream>
 #include <string>
 #include <variant>
 #include <vector>
@@ -163,7 +166,13 @@ struct Config {
  * comments.
  *
  * Syntax:
- * See tests/functional/repl_characterization/README.md.
+ * ```
+ * ( COMMENTARY
+ * | INDENT PROMPT COMMAND
+ * | INDENT OUTPUT
+ * | @args ARGS
+ * | @should-start ( true | false )) *
+ * ```
  *
  * e.g.
  * ```