diff --git a/.version-bump.json b/.version-bump.json
index 7fc6cc9f..8b9c6d99 100644
--- a/.version-bump.json
+++ b/.version-bump.json
@@ -1,6 +1,7 @@
 {
   "files": [
     { "path": "package.json", "field": "version" },
+    { "path": ".hermes-plugin/plugin.yaml", "field": "version" },
     { "path": ".claude-plugin/plugin.json", "field": "version" },
     { "path": ".cursor-plugin/plugin.json", "field": "version" },
     { "path": ".codex-plugin/plugin.json", "field": "version" },
diff --git a/scripts/bump-version.sh b/scripts/bump-version.sh
index 01adec99..14ead002 100755
--- a/scripts/bump-version.sh
+++ b/scripts/bump-version.sh
@@ -40,12 +40,72 @@ write_json_field() {
   jq "$jq_path = \"$value\"" "$file" > "$tmp" && mv "$tmp" "$file"
 }
 
+require_tool() {
+  command -v "$1" >/dev/null 2>&1 || {
+    echo "error: required tool '$1' is not on PATH" >&2
+    return 1
+  }
+}
+
+read_yaml_field() {
+  local file="$1" field="$2"
+  require_tool yq || return 1
+  FIELD="$field" yq -er '.[strenv(FIELD)] | select(tag == "!!str")' "$file"
+}
+
+write_yaml_field() {
+  local file="$1" field="$2" value="$3"
+  FIELD="$field" VALUE="$value" \
+    yq -i '.[strenv(FIELD)] = strenv(VALUE)' "$file"
+}
+
+read_manifest_field() {
+  local file="$1"
+
+  case "$file" in
+    *.json) read_json_field "$@" ;;
+    *.yaml) read_yaml_field "$@" ;;
+    *)
+      echo "error: unsupported manifest format: $file" >&2
+      return 1
+      ;;
+  esac
+}
+
+write_manifest_field() {
+  local file="$1"
+
+  case "$file" in
+    *.json) write_json_field "$@" ;;
+    *.yaml) write_yaml_field "$@" ;;
+    *)
+      echo "error: unsupported manifest format: $file" >&2
+      return 1
+      ;;
+  esac
+}
+
 # Read the list of declared files from config.
 # Outputs lines of "path<TAB>field"
 declared_files() {
   jq -r '.files[] | "\(.path)\t\(.field)"' "$CONFIG"
 }
 
+preflight_manifests() {
+  local path field fullpath
+
+  require_tool jq || return 1
+  while IFS=$'\t' read -r path field; do
+    fullpath="$REPO_ROOT/$path"
+    [[ -f "$fullpath" ]] || continue
+
+    if ! read_manifest_field "$fullpath" "$field" >/dev/null; then
+      echo "error: cannot read declared manifest: $path ($field)" >&2
+      return 1
+    fi
+  done < <(declared_files)
+}
+
 # Read the audit exclude patterns from config.
 audit_excludes() {
   jq -r '.audit.exclude[]' "$CONFIG" 2>/dev/null
@@ -68,7 +128,7 @@ cmd_check() {
       continue
     fi
     local ver
-    ver=$(read_json_field "$fullpath" "$field")
+    ver=$(read_manifest_field "$fullpath" "$field")
     printf "  %-45s  %s\n" "$path ($field)" "$ver"
     versions+=("$ver")
   done < <(declared_files)
@@ -101,7 +161,7 @@ cmd_audit() {
   current_version=$(
     while IFS=$'\t' read -r path field; do
       local fullpath="$REPO_ROOT/$path"
-      [[ -f "$fullpath" ]] && read_json_field "$fullpath" "$field"
+      [[ -f "$fullpath" ]] && read_manifest_field "$fullpath" "$field"
     done < <(declared_files) | sort | uniq -c | sort -rn | head -1 | awk '{print $2}'
   )
 
@@ -172,6 +232,8 @@ cmd_bump() {
     exit 1
   fi
 
+  preflight_manifests
+
   echo "Bumping all declared files to $new_version..."
   echo ""
 
@@ -182,8 +244,8 @@ cmd_bump() {
       continue
     fi
     local old_ver
-    old_ver=$(read_json_field "$fullpath" "$field")
-    write_json_field "$fullpath" "$field" "$new_version"
+    old_ver=$(read_manifest_field "$fullpath" "$field")
+    write_manifest_field "$fullpath" "$field" "$new_version"
     printf "  %-45s  %s -> %s\n" "$path ($field)" "$old_ver" "$new_version"
   done < <(declared_files)
 
diff --git a/tests/version-bump/test-bump-version.sh b/tests/version-bump/test-bump-version.sh
new file mode 100644
index 00000000..195d88a1
--- /dev/null
+++ b/tests/version-bump/test-bump-version.sh
@@ -0,0 +1,76 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
+REPO_ROOT="$(cd "$SCRIPT_DIR/../.." && pwd)"
+SCRIPT_SOURCE="$REPO_ROOT/scripts/bump-version.sh"
+TEST_ROOT="$(mktemp -d)"
+
+cleanup() {
+  rm -rf "$TEST_ROOT"
+}
+trap cleanup EXIT
+
+fail() {
+  echo "FAIL: $*" >&2
+  exit 1
+}
+
+make_fixture() {
+  local repo="$1"
+  local yaml_body="$2"
+
+  mkdir -p "$repo/scripts" "$repo/.hermes-plugin"
+  cp "$SCRIPT_SOURCE" "$repo/scripts/bump-version.sh"
+  cat >"$repo/.version-bump.json" <<'JSON'
+{
+  "files": [
+    { "path": "package.json", "field": "version" },
+    { "path": ".hermes-plugin/plugin.yaml", "field": "version" }
+  ],
+  "audit": { "exclude": [] }
+}
+JSON
+  cat >"$repo/package.json" <<'JSON'
+{
+  "name": "fixture",
+  "version": "1.2.3"
+}
+JSON
+  printf '%s\n' "$yaml_body" >"$repo/.hermes-plugin/plugin.yaml"
+}
+
+happy_repo="$TEST_ROOT/happy"
+make_fixture "$happy_repo" $'name: superpowers\nversion: 1.2.3'
+
+/bin/bash "$happy_repo/scripts/bump-version.sh" --check >"$TEST_ROOT/check.out"
+/bin/bash "$happy_repo/scripts/bump-version.sh" --audit >"$TEST_ROOT/audit.out"
+/bin/bash "$happy_repo/scripts/bump-version.sh" 2.3.4 >"$TEST_ROOT/bump.out"
+
+[[ "$(jq -r '.version' "$happy_repo/package.json")" == "2.3.4" ]] \
+  || fail "JSON manifest was not bumped"
+[[ "$(yq -r '.version' "$happy_repo/.hermes-plugin/plugin.yaml")" == "2.3.4" ]] \
+  || fail "YAML manifest was not bumped"
+
+jq -e '
+  any(.files[];
+    .path == ".hermes-plugin/plugin.yaml" and .field == "version")
+' "$REPO_ROOT/.version-bump.json" >/dev/null \
+  || fail "Hermes manifest is not registered"
+
+invalid_repo="$TEST_ROOT/invalid"
+make_fixture "$invalid_repo" $'name: superpowers\nversion: 123'
+cp "$invalid_repo/package.json" "$TEST_ROOT/package.before"
+cp "$invalid_repo/.hermes-plugin/plugin.yaml" "$TEST_ROOT/plugin.before"
+
+if /bin/bash "$invalid_repo/scripts/bump-version.sh" 2.3.4 \
+  >"$TEST_ROOT/invalid.out" 2>&1; then
+  fail "bump accepted a non-string YAML version"
+fi
+
+cmp -s "$TEST_ROOT/package.before" "$invalid_repo/package.json" \
+  || fail "JSON manifest changed before YAML validation failed"
+cmp -s "$TEST_ROOT/plugin.before" "$invalid_repo/.hermes-plugin/plugin.yaml" \
+  || fail "invalid YAML manifest changed"
+
+echo "Version-bump tests passed"