diff --git a/README.md b/README.md
index 49ee8ac..b37ad16 100644
--- a/README.md
+++ b/README.md
@@ -477,6 +477,8 @@ git gtr config set gtr.ui.color never
 
 **Adapter safety:** Generic `gtr.editor.default` and `gtr.ai.default` values must resolve to safe PATH commands. Filesystem paths such as `./tool` and shell wrapper forms such as `sh -c ...` are rejected. Override-backed adapters like `claude`, `cursor`, and `nano` may include additional flags, for example `claude --continue` or `nano -w`.
 
+**Worktree naming:** `gtr.worktrees.prefix` is a folder-name prefix, such as `dev-`, and cannot contain `/` or `\`. Set `gtr.worktrees.dir` to choose the parent directory. See [worktree settings](docs/configuration.md#worktree-settings).
+
 **Workspace files:** `editor.workspace` in `.gtrconfig` does not require command approval. Workspace paths from all config sources must resolve inside the selected worktree, including symlink targets; invalid paths open the folder instead. See [workspace settings](docs/configuration.md#editor-settings) for supported paths and editor trust boundaries.
 
 **Configuration precedence** (highest to lowest):
diff --git a/docs/configuration.md b/docs/configuration.md
index 3514cd5..92ff90a 100644
--- a/docs/configuration.md
+++ b/docs/configuration.md
@@ -97,7 +97,7 @@ gtr.worktrees.dir = .worktrees
 # Home directory (tilde expansion)
 gtr.worktrees.dir = ~/worktrees/my-project
 
-# Folder prefix (default: "")
+# Folder name prefix, without / or \ (default: "")
 gtr.worktrees.prefix = dev-
 
 # Default branch (default: auto-detect)
@@ -107,6 +107,13 @@ gtr.defaultBranch = main
 gtr.defaultRemote = upstream
 ```
 
+The prefix is prepended literally to the sanitized folder name: `dev-` and
+`feature/auth` produce `dev-feature-auth`. Empty prefixes are supported. Prefixes
+containing `/` or `\` are rejected from every configuration source, including
+`.gtrconfig` and `GTR_WORKTREES_PREFIX`. Use `gtr.worktrees.dir` to select a parent
+directory; for example, replace a `team/dev-` prefix with a `dev-` prefix and a
+base directory ending in `team`.
+
 > [!IMPORTANT]
 > If storing worktrees inside the repository, add the directory to `.gitignore`.
 
diff --git a/lib/commands/help.sh b/lib/commands/help.sh
index 8589800..3db5f5a 100644
--- a/lib/commands/help.sh
+++ b/lib/commands/help.sh
@@ -750,7 +750,7 @@ WORKFLOW EXAMPLES:
 CONFIGURATION OPTIONS:
 
   gtr.worktrees.dir        Worktrees base directory
-  gtr.worktrees.prefix     Worktree folder prefix (default: "")
+  gtr.worktrees.prefix     Folder name prefix, no / or \ (default: "")
   gtr.defaultBranch        Default branch (default: auto)
   gtr.defaultRemote        Default remote (default: origin)
   gtr.editor.default       Default editor
diff --git a/lib/core.sh b/lib/core.sh
index b13691c..1d49494 100644
--- a/lib/core.sh
+++ b/lib/core.sh
@@ -35,6 +35,18 @@ sanitize_branch_name() {
   printf "%s" "$branch" | sed -e 's/[\/\\ :*?"<>|#]/-/g' -e 's/^-*//' -e 's/-*$//'
 }
 
+# Prefixes name folders; worktrees.dir selects their parent directory.
+# Reject both POSIX and Windows separators instead of changing configured names.
+_validate_worktree_prefix() {
+  case "$1" in
+    */*|*\\*)
+      log_error "Invalid gtr.worktrees.prefix: path separators are not allowed; use gtr.worktrees.dir for directories"
+      return 1
+      ;;
+  esac
+  return 0
+}
+
 # Canonicalize a path to its absolute form, resolving symlinks
 # Usage: canonicalize_path path
 # Returns: canonical path or empty string on failure
@@ -420,6 +432,8 @@ resolve_target() {
       ;;
   esac
 
+  _validate_worktree_prefix "$prefix" || return 1
+
   # Special case: ID 1 is always the repo root
   if [ "$identifier" = "1" ]; then
     branch=$(get_current_branch "$repo_root") || return 1
@@ -827,6 +841,8 @@ create_worktree() {
   local no_checkout="${11:-0}"
   local add_source="${12:-}"
 
+  _validate_worktree_prefix "$prefix" || return 1
+
   local sanitized_name
   sanitized_name=$(_resolve_folder_name "$branch_name" "$custom_name" "$folder_override") || return 1
 
@@ -957,6 +973,7 @@ resolve_repo_context() {
   _ctx_repo_root=$(discover_repo_root) || return 1
   _ctx_base_dir=$(resolve_base_dir "$_ctx_repo_root")
   _ctx_prefix=$(cfg_default gtr.worktrees.prefix GTR_WORKTREES_PREFIX "")
+  _validate_worktree_prefix "$_ctx_prefix" || return 1
 }
 
 # List all worktree branch names (excluding main repo)
diff --git a/tests/cmd_create_integration.bats b/tests/cmd_create_integration.bats
index 81150d1..b1f345d 100644
--- a/tests/cmd_create_integration.bats
+++ b/tests/cmd_create_integration.bats
@@ -28,6 +28,78 @@ _cmd_create_capture_stdout() {
   [ -d "$TEST_WORKTREES_DIR/new-feature" ]
 }
 
+@test "cmd_create accepts an untrusted folder prefix with sanitized branch and custom names" {
+  git config -f .gtrconfig worktrees.prefix dev-
+  [ ! -d "$_GTR_TRUST_DIR" ]
+
+  run "$PROJECT_ROOT/bin/gtr" new feature/auth --name backend --from HEAD --no-fetch --no-copy --no-hooks --yes
+  [ "$status" -eq 0 ]
+  [ -f "$TEST_WORKTREES_DIR/dev-feature-auth-backend/.git" ]
+
+  run "$PROJECT_ROOT/bin/gtr" new review --folder chosen --from HEAD --no-fetch --no-copy --no-hooks --yes
+  [ "$status" -eq 0 ]
+  [ -f "$TEST_WORKTREES_DIR/dev-chosen/.git" ]
+  [ ! -d "$_GTR_TRUST_DIR" ]
+}
+
+@test "cmd_create rejects traversal prefixes from shared local global and environment config" {
+  local source base_dir="$TEST_REPO/prefix-fixture/trees"
+  mkdir -p "$TEST_REPO/prefix-fixture"
+  git config gtr.worktrees.dir "$base_dir"
+  export GIT_CONFIG_GLOBAL="$TEST_REPO/prefix-global-config"
+  for source in shared local global environment; do
+    case "$source" in
+      shared)
+        git config -f .gtrconfig worktrees.prefix ../planted-
+        git add .gtrconfig
+        git commit -m "shared prefix" --quiet
+        ;;
+      local) git config gtr.worktrees.prefix ../planted- ;;
+      global) git config --global gtr.worktrees.prefix ../planted- ;;
+      environment) export GTR_WORKTREES_PREFIX=../planted- ;;
+    esac
+
+    run "$PROJECT_ROOT/bin/gtr" new rejected-prefix --from HEAD --no-fetch --no-copy --no-hooks --yes
+    [ "$status" -eq 1 ]
+    [[ "$output" == *"Invalid gtr.worktrees.prefix"* ]]
+    [ ! -e "$base_dir" ]
+    [ ! -e "$TEST_REPO/prefix-fixture/planted-rejected-prefix" ]
+    ! git show-ref --verify --quiet refs/heads/rejected-prefix
+    [ ! -d "$_GTR_TRUST_DIR" ]
+
+    case "$source" in
+      shared) git config -f .gtrconfig --unset worktrees.prefix ;;
+      local) git config --unset gtr.worktrees.prefix ;;
+      global) git config --global --unset gtr.worktrees.prefix ;;
+      environment) unset GTR_WORKTREES_PREFIX ;;
+    esac
+  done
+}
+
+@test "cmd_create validates the effective prefix after config precedence" {
+  git config -f .gtrconfig worktrees.prefix ../planted-
+  git config gtr.worktrees.prefix dev-
+
+  run "$PROJECT_ROOT/bin/gtr" new safe-override --from HEAD --no-fetch --no-copy --no-hooks --yes
+
+  [ "$status" -eq 0 ]
+  [ -f "$TEST_WORKTREES_DIR/dev-safe-override/.git" ]
+}
+
+@test "cmd_create rejects invalid prefixes without emitting porcelain records" {
+  git config gtr.worktrees.dir "$TEST_REPO/prefix-fixture/trees"
+  git config gtr.worktrees.prefix '../planted-'
+  local stdout_file="$TEST_REPO/prefix-stdout" stderr_file="$TEST_REPO/prefix-stderr"
+
+  run bash -c '"$1" new rejected-prefix --from HEAD --no-fetch --porcelain >"$2" 2>"$3"' \
+    _ "$PROJECT_ROOT/bin/gtr" "$stdout_file" "$stderr_file"
+
+  [ "$status" -eq 1 ]
+  [ ! -s "$stdout_file" ]
+  grep -q "Invalid gtr.worktrees.prefix" "$stderr_file"
+  ! git show-ref --verify --quiet refs/heads/rejected-prefix
+}
+
 @test "cmd_create treats untrusted defaults.remote as a fetch operand" {
   # Every remote is local; --all must not cause an unrelated remote to be fetched.
   git remote add origin "$TEST_REPO"
diff --git a/tests/cmd_pr.bats b/tests/cmd_pr.bats
index ed703ad..0e5fb63 100644
--- a/tests/cmd_pr.bats
+++ b/tests/cmd_pr.bats
@@ -75,6 +75,44 @@ teardown() {
   [ "$(git config branch.review/pr-123.merge)" = "refs/heads/feature/from-pr" ]
 }
 
+@test "cmd_pr fallback applies an ordinary folder prefix" {
+  git config -f .gtrconfig worktrees.prefix dev-
+
+  cmd_pr 123 --remote origin --no-copy --no-hooks --yes
+
+  [ -f "$TEST_WORKTREES_DIR/dev-feature-from-pr/.git" ]
+  [ "$(git -C "$TEST_WORKTREES_DIR/dev-feature-from-pr" rev-parse HEAD)" = "$TEST_PR_SHA" ]
+}
+
+@test "cmd_pr rejects traversal prefixes before native checkout or fallback fetch" {
+  git config gtr.worktrees.dir "$TEST_REPO/prefix-fixture/trees"
+  git config -f .gtrconfig worktrees.prefix ../planted-
+  export TEST_GH_LOG="$TEST_MOCK_BIN/gh.log"
+  cat > "$TEST_MOCK_BIN/gh" <<'SCRIPT'
+#!/usr/bin/env bash
+printf '%s\n' "$*" >> "$TEST_GH_LOG"
+if [ "$1" = "pr" ] && [ "$2" = "checkout" ] && [ "$3" = "--help" ]; then
+  printf '      --worktree path\n'
+elif [ "$1" = "pr" ] && [ "$2" = "view" ]; then
+  printf '123\tfeature/from-pr\tocto\texample\thttps://github.com/base/example/pull/123\ttrue\ttrue\n'
+fi
+SCRIPT
+  local mode
+  for mode in native fallback; do
+    local args=()
+    [ "$mode" = "fallback" ] && args=(--remote origin)
+
+    run "$PROJECT_ROOT/bin/gtr" pr 123 "${args[@]}" --no-copy --no-hooks --yes
+
+    [ "$status" -eq 1 ]
+    [[ "$output" == *"Invalid gtr.worktrees.prefix"* ]]
+    [ ! -e "$TEST_GH_LOG" ]
+    [ ! -e "$TEST_REPO/prefix-fixture" ]
+    [ ! -e "$TEST_REPO/.git/FETCH_HEAD" ]
+    ! git show-ref --verify --quiet refs/heads/feature/from-pr
+  done
+}
+
 @test "cmd_pr reuses ssh remote matching resolved PR base repository" {
   git remote add upstream git@github.com:base/example.git
 
@@ -130,6 +168,7 @@ SCRIPT
 }
 
 @test "cmd_pr delegates worktree creation to gh when supported" {
+  git config gtr.worktrees.prefix dev-
   export TEST_GH_LOG="$TEST_MOCK_BIN/gh.log"
   cat > "$TEST_MOCK_BIN/gh" <<'SCRIPT'
 #!/usr/bin/env bash
@@ -159,12 +198,12 @@ SCRIPT
 
   cmd_pr 123 --no-copy --no-hooks --yes
 
-  [ -d "$TEST_WORKTREES_DIR/feature-from-pr" ]
+  [ -d "$TEST_WORKTREES_DIR/dev-feature-from-pr" ]
   local logged_path logged_branch
   IFS=$'\t' read -r logged_path logged_branch < "$TEST_GH_LOG"
-  [ "${logged_path##*/}" = "feature-from-pr" ]
+  [ "${logged_path##*/}" = "dev-feature-from-pr" ]
   [ "$logged_branch" = "feature/from-pr" ]
-  [ "$(git -C "$TEST_WORKTREES_DIR/feature-from-pr" rev-parse HEAD)" = "$TEST_PR_SHA" ]
+  [ "$(git -C "$TEST_WORKTREES_DIR/dev-feature-from-pr" rev-parse HEAD)" = "$TEST_PR_SHA" ]
 }
 
 @test "cmd_pr fetches the resolved PR base repository by default" {
diff --git a/tests/cmd_rename.bats b/tests/cmd_rename.bats
index 354285e..d417a59 100644
--- a/tests/cmd_rename.bats
+++ b/tests/cmd_rename.bats
@@ -32,6 +32,33 @@ teardown() {
   [ "$status" -ne 0 ]
 }
 
+@test "cmd_rename preserves an ordinary folder prefix" {
+  git config gtr.worktrees.prefix dev-
+  create_worktree "$TEST_WORKTREES_DIR" "dev-" "old-name" "HEAD" "none" "1" >/dev/null
+
+  cmd_rename old-name feature/renamed --yes
+
+  [ -f "$TEST_WORKTREES_DIR/dev-feature-renamed/.git" ]
+  [ ! -e "$TEST_WORKTREES_DIR/dev-old-name" ]
+  [ "$(get_current_branch "$TEST_WORKTREES_DIR/dev-feature-renamed")" = "feature/renamed" ]
+}
+
+@test "cmd_rename rejects traversal prefixes without moving the worktree or renaming its branch" {
+  create_test_worktree "old-name"
+  local old_path="$TEST_WT_PATH"
+  git config gtr.worktrees.dir "$TEST_REPO/prefix-fixture/trees"
+  git config -f .gtrconfig worktrees.prefix ../planted-
+
+  run "$PROJECT_ROOT/bin/gtr" mv old-name renamed --yes
+
+  [ "$status" -eq 1 ]
+  [[ "$output" == *"Invalid gtr.worktrees.prefix"* ]]
+  [ -f "$old_path/.git" ]
+  [ "$(get_current_branch "$old_path")" = "old-name" ]
+  [ ! -e "$TEST_REPO/prefix-fixture" ]
+  ! git show-ref --verify --quiet refs/heads/renamed
+}
+
 # ── Error cases ──────────────────────────────────────────────────────────────
 
 @test "cmd_rename fails with insufficient args" {
diff --git a/tests/core_create_worktree.bats b/tests/core_create_worktree.bats
index 7ce3709..a8b34e9 100644
--- a/tests/core_create_worktree.bats
+++ b/tests/core_create_worktree.bats
@@ -166,6 +166,31 @@ teardown() {
   [ -d "$wt_path" ]
 }
 
+@test "create_worktree preserves empty dotted and spaced folder prefixes" {
+  local prefix wt_path index=0
+  for prefix in "" "dev-" "." ".." "my team-"; do
+    wt_path=$(create_worktree "$TEST_WORKTREES_DIR" "$prefix" "prefix-$index" "HEAD" "none" "1")
+    [ "$wt_path" = "$TEST_WORKTREES_DIR/${prefix}prefix-$index" ]
+    [ -f "$wt_path/.git" ]
+    index=$((index + 1))
+  done
+}
+
+@test "create_worktree rejects prefix path separators before creating directories or branches" {
+  # Even a regression can only create destinations inside this disposable repo.
+  local base_dir="$TEST_REPO/prefix-fixture/trees" prefix
+  mkdir -p "$TEST_REPO/prefix-fixture"
+  for prefix in "../planted-" "group/../../planted-" "group/dev-" "/absolute-" \
+      '..\planted-' 'group\dev-' 'C:\dev-'; do
+    run create_worktree "$base_dir" "$prefix" "rejected-prefix" "HEAD" "none" "1"
+    [ "$status" -eq 1 ]
+    [[ "$output" == *"Invalid gtr.worktrees.prefix"* ]]
+    [ ! -e "$base_dir" ]
+    [ ! -e "$TEST_REPO/prefix-fixture/planted-rejected-prefix" ]
+    ! git show-ref --verify --quiet refs/heads/rejected-prefix
+  done
+}
+
 @test "create_worktree applies custom name suffix" {
   local wt_path
   wt_path=$(create_worktree "$TEST_WORKTREES_DIR" "" "feature" "HEAD" "none" "1" "0" "backend")
diff --git a/tests/core_resolve_target.bats b/tests/core_resolve_target.bats
index 3074bac..73e6549 100644
--- a/tests/core_resolve_target.bats
+++ b/tests/core_resolve_target.bats
@@ -52,6 +52,16 @@ teardown() {
   [[ "$result" == "0"$'\t'"$TEST_WORKTREES_DIR/wt-prefixed"* ]]
 }
 
+@test "resolve_target rejects traversal prefixes even when the destination exists" {
+  local base_dir="$TEST_REPO/prefix-fixture/trees"
+  mkdir -p "$base_dir" "$TEST_REPO/prefix-fixture/planted-feature"
+
+  run resolve_target "feature" "$TEST_REPO" "$base_dir" "../planted-"
+
+  [ "$status" -eq 1 ]
+  [[ "$output" == *"Invalid gtr.worktrees.prefix"* ]]
+}
+
 @test "resolve_target rejects a sanitized collision with a different branch" {
   create_test_worktree "feat-login"