Answer product-owner round 1: the hint for an empty stdin points to --list, the help's examples are templates only, the README's record id is an integer, and a test over an indexed module renders each path

README.md

@@ -352,7 +352,7 @@ v = t.Fake()                                              // render many times,
 r, err := f.FakeRecord("users")           // one record: each field a column
 s := r.JSON()                             // {"first":"Ada","last":"Lovelace"}
 r, err = f.FakeRecordTemplate(`{"format":"{x}","x":["a","b"]}`) // compile + render inline
-rt, err := f.NewRecordTemplate(`{"format":"","id":"{seq(users)}"}`) // compile a record once
+rt, err := f.NewRecordTemplate(`{"format":"","id":{"format":"{seq(users)}","datatype":"integer"}}`) // compile once
 r = rt.Fake()                             // render a row; loop this for bulk output
 err = f.FakeStruct(&user)                 // fill a struct's fake:"…" tagged fields
 ok, err := fejkdata.IsTemplate(arg)       // an inline template by its shape, else a path
@@ -459,7 +459,8 @@ func main() { os.Exit(cli.Main(append(data.Modules(), mydata)...)) }
 The embed's folders are the paths: `//go:embed acme` serves `acme/customer.json` as
 `{/acme.customer}`. Add `*.tsv` to the embed where your data holds a table. The CLI loads
 its data when it runs, so a test calling `fejkdata.New(fejkdata.WithDataFS(...))` over the
-same modules catches broken data at `go test`. The CLI takes `fejkdata`'s flags
+same modules, rendering each path once where a module carries an index, catches broken
+data at `go test`. The CLI takes `fejkdata`'s flags
 and exit codes, and names itself by the file it runs from in its help and errors. `--no-shipped-data` leaves out the modules passed to `Main`, and
 `--version` prints your module's version beside the fejkdata version it is built with.
 

cli/cli.go

@@ -29,7 +29,6 @@ COMMAND reads one template from stdin and renders it:
 
   echo 'id: {int(1,999)}' | COMMAND
   echo '{"format":"{x}","x":["bosse","lina"]}' | COMMAND
-  COMMAND --list                     # the paths a {/path} reference reads
   COMMAND < template.txt
 
 COMMAND <<'EOF'
@@ -630,7 +629,7 @@ func run(name string, modules []fs.FS, args []string, stdin io.Reader, stdout, s
 
 func readStdin(stdin io.Reader, name string) (input, error) {
 	if stdin == nil {
-		return input{}, inputError{fmt.Errorf("the template comes from stdin, and nothing is piped in: %s", pipeHint(name))}
+		return input{}, inputError{fmt.Errorf("the template comes from stdin, and nothing is piped in: %s; %s --list prints the paths a {/path} reference reads", pipeHint(name), name)}
 	}
 	raw, err := io.ReadAll(stdin)
 	if err != nil {