diff --git a/cpp/ql/test/justfile b/cpp/ql/test/justfile
index a3d05a28814..3c7143ef7cb 100644
--- a/cpp/ql/test/justfile
+++ b/cpp/ql/test/justfile
@@ -2,10 +2,11 @@ import "../justfile"
 
 base_flags := "--include-location-in-star"
 
-all_checks := default_db_checks + """\
+all_checks := f"""\
+    {{default_db_checks}}\
     --check-undefined-labels \
     --check-unused-labels \
-    --consistency-queries=""" + consistency_queries
+    --consistency-queries={{consistency_queries}}"""
 
 [no-cd]
 test *ARGS=".": (_codeql_test "cpp" base_flags all_checks ARGS)
diff --git a/csharp/ql/test/justfile b/csharp/ql/test/justfile
index 0c0332ddb48..fbd9884a4cf 100644
--- a/csharp/ql/test/justfile
+++ b/csharp/ql/test/justfile
@@ -2,12 +2,13 @@ import "../justfile"
 
 base_flags := ""
 
-all_checks := default_db_checks + """\
+all_checks := f"""\
+    {{default_db_checks}}\
     --check-undefined-labels \
     --check-repeated-labels \
     --check-redefined-labels \
     --additional-packs=ql \
-    --consistency-queries=""" + consistency_queries
+    --consistency-queries={{consistency_queries}}"""
 
 [no-cd]
 test *ARGS=".": (_codeql_test "csharp" base_flags all_checks ARGS)
diff --git a/go/ql/test/justfile b/go/ql/test/justfile
index 5c1fe5d71fd..d85eaf538cd 100644
--- a/go/ql/test/justfile
+++ b/go/ql/test/justfile
@@ -2,13 +2,14 @@ import "../justfile"
 
 base_flags := ""
 
-all_checks := default_db_checks + """\
+all_checks := f"""\
+    {{default_db_checks}}\
     --check-undefined-labels \
     --check-unused-labels \
     --check-repeated-labels \
     --check-redefined-labels \
     --check-use-before-definition \
-    --consistency-queries=""" + consistency_queries
+    --consistency-queries={{consistency_queries}}"""
 
 [no-cd]
 test *ARGS=".": (_codeql_test "go" base_flags all_checks ARGS)
diff --git a/java/ql/test-kotlin1/justfile b/java/ql/test-kotlin1/justfile
index 8e9ecc8c925..4dcc7171b2f 100644
--- a/java/ql/test-kotlin1/justfile
+++ b/java/ql/test-kotlin1/justfile
@@ -4,12 +4,13 @@ base_flags := """\
     CODEQL_EXTRACTOR_KOTLIN_DIAGNOSTIC_LIMIT= \
 """
 
-all_checks := default_db_checks + """\
+all_checks := f"""\
+    {{default_db_checks}}\
     --check-undefined-labels \
     --check-repeated-labels \
     --check-redefined-labels \
     --check-use-before-definition \
-    --consistency-queries=""" + consistency_queries
+    --consistency-queries={{consistency_queries}}"""
 
 [no-cd]
 test *ARGS=".": (_codeql_test "java" base_flags all_checks ARGS)
diff --git a/java/ql/test-kotlin2/justfile b/java/ql/test-kotlin2/justfile
index a1f3170e784..5b9e74f2fc4 100644
--- a/java/ql/test-kotlin2/justfile
+++ b/java/ql/test-kotlin2/justfile
@@ -5,12 +5,13 @@ base_flags := """\
     CODEQL_KOTLIN_LEGACY_TEST_EXTRACTION_KOTLIN2=true \
 """
 
-all_checks := default_db_checks + """\
+all_checks := f"""\
+    {{default_db_checks}}\
     --check-undefined-labels \
     --check-repeated-labels \
     --check-redefined-labels \
     --check-use-before-definition \
-    --consistency-queries=""" + consistency_queries
+    --consistency-queries={{consistency_queries}}"""
 
 [no-cd]
 test *ARGS=".": (_codeql_test "java" base_flags all_checks ARGS)
diff --git a/java/ql/test/justfile b/java/ql/test/justfile
index f31d7c3c213..f7805bd6418 100644
--- a/java/ql/test/justfile
+++ b/java/ql/test/justfile
@@ -4,12 +4,13 @@ base_flags := """\
      CODEQL_EXTRACTOR_KOTLIN_DIAGNOSTIC_LIMIT="\\ " \
 """
 
-all_checks := default_db_checks + """\
+all_checks := f"""\
+    {{default_db_checks}}\
     --check-undefined-labels \
     --check-repeated-labels \
     --check-redefined-labels \
     --check-use-before-definition \
-    --consistency-queries=""" + consistency_queries
+    --consistency-queries={{consistency_queries}}"""
 
 [no-cd]
 test *ARGS=".": (_codeql_test "java" base_flags all_checks ARGS)
diff --git a/misc/just/build.just b/misc/just/build.just
index 872159ee682..b798e980a63 100644
--- a/misc/just/build.just
+++ b/misc/just/build.just
@@ -8,7 +8,7 @@ _build_dist LANGUAGE: _require_semmle_code (_maybe_build_dist LANGUAGE)
 # Build the language-specific distribution if we are in an internal repository checkout
 # Otherwise, do nothing
 [no-exit-message]
-_maybe_build_dist LANGUAGE: (_if_in_semmle_code ('cd "$SEMMLE_CODE"; tools/bazel test //language-packs:intree-' + LANGUAGE + '-as-test --test_output=all') '# using codeql from PATH, if any')
+_maybe_build_dist LANGUAGE: (_if_in_semmle_code (f'cd "$SEMMLE_CODE"; tools/bazel test //language-packs:intree-{{LANGUAGE}}-as-test --test_output=all') '# using codeql from PATH, if any')
 
 # Call bazel. Uses our official bazel wrapper if we are in an internal repository checkout
 [no-cd, no-exit-message]
diff --git a/misc/just/defs.just b/misc/just/defs.just
index 71cba34e1a7..cbf9171188b 100644
--- a/misc/just/defs.just
+++ b/misc/just/defs.just
@@ -4,12 +4,11 @@ import 'semmle-code-stub.just'
 set fallback
 set allow-duplicate-recipes
 set allow-duplicate-variables
-set unstable
 
 export PATH_SEP := if os() == "windows" { ";" } else { ":" }
 export JUST_EXECUTABLE := just_executable()
 
-error := style("error") + "error" + NORMAL + ": "
+error := f'{{style("error")}}error{{NORMAL}}: '
 cmd_sep := "\n#--------------------------------------------------------\n"
 export CMD_BEGIN := style("command") + cmd_sep
 export CMD_END := cmd_sep + NORMAL
@@ -25,8 +24,8 @@ default_db_checks := """\
 
 [no-exit-message]
 @_require_semmle_code:
-    {{ if SEMMLE_CODE == "" { '''
-        echo "''' + error + ''' running this recipe requires doing so from an internal repository checkout" >&2
+    {{ if SEMMLE_CODE == "" { f'''
+        echo "{error} running this recipe requires doing so from an internal repository checkout" >&2
         exit 1
     ''' } else { "" } }}
 
diff --git a/misc/just/format.just b/misc/just/format.just
index 9430cb4c0a9..13ade85c1cb 100644
--- a/misc/just/format.just
+++ b/misc/just/format.just
@@ -5,7 +5,7 @@ _format_ql +ARGS: (_maybe_build_dist "nolang") (
     _if_in_semmle_code
         '"$SEMMLE_CODE/target/intree/codeql-nolang/codeql"'
         'codeql'
-    ("query format --in-place -v $(find " + ARGS + " -type f -name '*.ql' -or -name '*.qll')")
+    (f"query format --in-place -v $(find {{ARGS}} -type f -name '*.ql' -or -name '*.qll')")
 )
 
 [no-cd, no-exit-message]
@@ -16,5 +16,5 @@ _format_cpp *ARGS=".": (
     _if_in_semmle_code
         "uv run clang-format"
         "clang-format"
-    "-i --verbose $(find " + ARGS + " -type f -name '*.h' -or -name '*.cpp')"
+    (f"-i --verbose $(find {{ARGS}} -type f -name '*.h' -or -name '*.cpp')")
 )
diff --git a/misc/just/forward.just b/misc/just/forward.just
index 8dd83e28496..da7f58724e9 100644
--- a/misc/just/forward.just
+++ b/misc/just/forward.just
@@ -7,7 +7,7 @@ import "lib.just"
 # copy&paste necessary for each command until proper forwarding of multiple args is implemented
 # see https://github.com/casey/just/issues/1988
 
-_forward := py + ' "' + source_dir() + '/forward_command.py"'
+_forward := f'{{py}} "{{source_dir()}}/forward_command.py"'
 
 alias t := test
 alias b := build
diff --git a/python/ql/test/justfile b/python/ql/test/justfile
index eae85301f00..b203afd69c1 100644
--- a/python/ql/test/justfile
+++ b/python/ql/test/justfile
@@ -2,8 +2,9 @@ import "../justfile"
 
 base_flags := _python_env
 
-all_checks := default_db_checks + """\
-    --consistency-queries=""" + consistency_queries
+all_checks := f"""\
+    {{default_db_checks}}\
+    --consistency-queries={{consistency_queries}}"""
 
 [no-cd]
 test *ARGS=".": (_codeql_test "python" base_flags all_checks ARGS)
diff --git a/ruby/ql/test/justfile b/ruby/ql/test/justfile
index 180815a0a8d..9b594915f51 100644
--- a/ruby/ql/test/justfile
+++ b/ruby/ql/test/justfile
@@ -2,13 +2,14 @@ import "../justfile"
 
 base_flags := ""
 
-all_checks := default_db_checks + """\
+all_checks := f"""\
+    {{default_db_checks}}\
     --check-undefined-labels \
     --check-unused-labels \
     --check-repeated-labels \
     --check-redefined-labels \
     --check-use-before-definition \
-    --consistency-queries=""" + consistency_queries
+    --consistency-queries={{consistency_queries}}"""
 
 [no-cd]
 test *ARGS=".": (_codeql_test "ruby" base_flags all_checks ARGS)
diff --git a/rust/ql/test/justfile b/rust/ql/test/justfile
index 0b1b075fbbb..0336a86b697 100644
--- a/rust/ql/test/justfile
+++ b/rust/ql/test/justfile
@@ -1,7 +1,8 @@
 import "../justfile"
 
-all_checks := default_db_checks + """\
-     --consistency-queries=""" + consistency_queries
+all_checks := f"""\
+    {{default_db_checks}}\
+     --consistency-queries={{consistency_queries}}"""
 
 [no-cd]
 test *ARGS=".": (_codeql_test "rust" "" all_checks ARGS)
diff --git a/swift/justfile b/swift/justfile
index 72fa15c8156..88bf72f4c94 100644
--- a/swift/justfile
+++ b/swift/justfile
@@ -13,5 +13,5 @@ format ARGS=".": (_format_cpp ARGS)
 [group('test')]
 language-tests *EXTRA_ARGS: (_language_tests EXTRA_ARGS source_dir() 'ql/test')
 
-[group('test')]
+[group('test'), parallel]
 extra-tests: (_sembuild "target/test/check-queries-swift") (_sembuild "target/test/check-db-upgrades-swift") (_sembuild "target/test/check-db-downgrades-swift")
diff --git a/swift/ql/test/justfile b/swift/ql/test/justfile
index b27ef6f52ed..34afe878f00 100644
--- a/swift/ql/test/justfile
+++ b/swift/ql/test/justfile
@@ -1,10 +1,11 @@
 import "../justfile"
 
-all_checks := default_db_checks + """\
+all_checks := f"""\
+    {{default_db_checks}}\
     --check-repeated-labels \
     --check-redefined-labels \
     --check-use-before-definition \
-    --consistency-queries=""" + consistency_queries
+    --consistency-queries={{consistency_queries}}"""
 
 
 [no-cd]