diff --git a/CHANGELOG.md b/CHANGELOG.md
index f9d479a..d952066 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,10 @@
 
 ## [Unreleased]
 
+### Added
+
+- The `bump-package-json` option (default: `false`) sets the `version` field of the root `package.json` to the release version.
+
 ## [1.1.0] - 2026-08-09
 
 ### Added
diff --git a/README.adoc b/README.adoc
index 7995f51..f24a72f 100644
--- a/README.adoc
+++ b/README.adoc
@@ -117,8 +117,9 @@ jobs:
 |===
 | Input | Default | Description
 
-| `version-file` | `''` | Path to a file to overwrite with the version. Leave empty to skip.
-| `keep-v-prefix` | `false` | When `true`, writes the tag verbatim. Otherwise strips the leading `v`.
+| `version-file` | `''` | Path to a file to overwrite with the version. Leave empty to skip. Not for JSON manifests: the file is replaced wholesale, so use `bump-package-json` for those.
+| `keep-v-prefix` | `false` | When `true`, writes the tag verbatim. Otherwise strips the leading `v`. Does not apply to `bump-package-json`.
+| `bump-package-json` | `false` | When `true`, sets the `version` field of the root `package.json`, leaving the rest of the manifest byte-for-byte intact. The leading `v` is always stripped, as npm requires plain semver.
 |===
 
 === Changelog
@@ -156,7 +157,7 @@ jobs:
 |===
 | Input | Default | Description
 
-| `commit` | `false` | Commit the modified `version-file` and `changelog-file` back to a branch.
+| `commit` | `false` | Commit the modified `version-file`, `changelog-file` and `package.json` back to a branch.
 | `commit-message` | `+chore: release {tag}+` | `+{tag}+` is substituted with the tag.
 | `commit-user-name` | `github-actions` | Name used for the auto-commit author.
 | `commit-user-email` | `+github-actions[bot]@users.noreply.github.com+` | Email used for the auto-commit author.
diff --git a/action.yml b/action.yml
index b2250d7..bfe97de 100644
--- a/action.yml
+++ b/action.yml
@@ -45,7 +45,20 @@ inputs:
   keep-v-prefix:
     description: >
       When `true`, the tag is written to `version-file` verbatim. When `false`
-      (default), the leading `v` is stripped.
+      (default), the leading `v` is stripped. Does not affect
+      `bump-package-json`, whose version must remain plain semver.
+    required: false
+    default: 'false'
+
+  bump-package-json:
+    description: >
+      When `true`, sets the `version` field of `package.json` in the repository
+      root to the release version, leaving the rest of the manifest untouched.
+      Use this instead of `version-file` for npm-shaped projects: `version-file`
+      overwrites its target with the bare version string, which would destroy a
+      JSON manifest. The leading `v` is always stripped, since npm requires
+      plain semver. The manifest is included in the commit when `commit` is
+      `true`.
     required: false
     default: 'false'
 
@@ -101,8 +114,8 @@ inputs:
   # Commit updates back
   commit:
     description: >
-      When `true`, commits changes to `version-file` and `changelog-file` back
-      to the repository.
+      When `true`, commits changes to `version-file`, `changelog-file` and, when
+      `bump-package-json` is enabled, `package.json` back to the repository.
     required: false
     default: 'false'
 
@@ -314,6 +327,15 @@ runs:
         args+=("$VERSION_FILE" "$TAG")
         "${GITHUB_ACTION_PATH}/scripts/bump-version.sh" "${args[@]}"
 
+    - name: Bump package.json
+      if: inputs.bump-package-json == 'true'
+      shell: bash
+      env:
+        TAG: ${{ steps.compute.outputs.tag }}
+      run: |
+        set -euo pipefail
+        "${GITHUB_ACTION_PATH}/scripts/bump-package-json.sh" package.json "$TAG"
+
     - name: Update changelog
       if: inputs.changelog-file != '' && inputs.update-changelog != 'false'
       uses: thomaseizinger/keep-a-changelog-new-release@v2
@@ -336,7 +358,9 @@ runs:
         commit_user_name: ${{ inputs.commit-user-name }}
         commit_user_email: ${{ inputs.commit-user-email }}
         file_pattern: >-
-          ${{ inputs.version-file }} ${{ inputs.changelog-file }}
+          ${{ inputs.version-file }}
+          ${{ inputs.bump-package-json == 'true' && 'package.json' || '' }}
+          ${{ inputs.changelog-file }}
         branch: ${{ inputs.commit-branch }}
 
     - name: Move devbuild tag
diff --git a/scripts/bump-package-json.sh b/scripts/bump-package-json.sh
new file mode 100755
index 0000000..7158e03
--- /dev/null
+++ b/scripts/bump-package-json.sh
@@ -0,0 +1,70 @@
+#!/usr/bin/env bash
+# Sets the `version` field of a package.json-style JSON manifest.
+#
+# Usage: bump-package-json.sh <manifest-file> <tag>
+#
+# The leading `v` is always stripped, unlike `bump-version.sh`: npm requires the
+# version field to be plain semver, so a `v`-prefixed value would be invalid.
+#
+# Only the version is rewritten. A manifest formatted the usual way keeps every
+# other byte, so the resulting commit touches a single line. A manifest whose
+# version cannot be located that way (unusual formatting, or no version field at
+# all) is re-serialized instead, which may reformat it.
+
+set -euo pipefail
+
+file="${1:-}"
+tag="${2:-}"
+
+if [ -z "$file" ]; then
+    echo "bump-package-json.sh: missing manifest path" >&2
+    exit 2
+fi
+
+if [ -z "$tag" ]; then
+    echo "bump-package-json.sh: missing tag" >&2
+    exit 2
+fi
+
+if [ ! -f "$file" ]; then
+    echo "bump-package-json.sh: manifest '$file' does not exist" >&2
+    exit 2
+fi
+
+if ! command -v node >/dev/null 2>&1; then
+    echo "bump-package-json.sh: node is required to edit '$file'" >&2
+    exit 2
+fi
+
+node -e '
+const fs = require("fs");
+const [file, tag] = process.argv.slice(1);
+const version = tag.replace(/^v/, "");
+const source = fs.readFileSync(file, "utf8");
+
+try {
+    JSON.parse(source);
+} catch (error) {
+    console.error(`bump-package-json.sh: ${file} is not valid JSON: ${error.message}`);
+    process.exit(2);
+}
+
+// Indentation of the first nested key, reused so the manifest keeps its shape.
+const indent = (source.match(/\n([ \t]+)"/) || [])[1] || "  ";
+
+// Anchoring to that indentation keeps the match at the top level, so a nested
+// "version" (in an engines block, say) is never mistaken for the manifest own.
+const topLevelVersion = new RegExp(`^${indent}"version"(\\s*:\\s*)"[^"]*"`, "m");
+
+let updated;
+if (topLevelVersion.test(source)) {
+    updated = source.replace(topLevelVersion, `${indent}"version"$1${JSON.stringify(version)}`);
+} else {
+    const manifest = JSON.parse(source);
+    manifest.version = version;
+    const trailingNewline = source.endsWith("\n") ? "\n" : "";
+    updated = JSON.stringify(manifest, null, indent) + trailingNewline;
+}
+
+fs.writeFileSync(file, updated);
+' "$file" "$tag"
diff --git a/tests/bump-package-json.bats b/tests/bump-package-json.bats
new file mode 100644
index 0000000..750eabd
--- /dev/null
+++ b/tests/bump-package-json.bats
@@ -0,0 +1,121 @@
+#!/usr/bin/env bats
+
+load 'test_helper'
+
+setup() {
+    setup_scripts_dir
+    setup_tmp_workspace
+    MANIFEST="$TMP_WORKSPACE/package.json"
+}
+
+teardown() {
+    teardown_tmp_workspace
+}
+
+# Writes a conventional two-space manifest to $MANIFEST.
+write_manifest() {
+    cat > "$MANIFEST" << 'JSON'
+{
+    "name": "example",
+    "version": "0.1.0",
+    "scripts": {
+        "build": "tsc"
+    }
+}
+JSON
+}
+
+@test "strips leading v and sets the version" {
+    write_manifest
+    run "$SCRIPTS_DIR/bump-package-json.sh" "$MANIFEST" "v1.2.3"
+    [ "$status" -eq 0 ]
+    [ "$(node -p "require('$MANIFEST').version")" = "1.2.3" ]
+}
+
+@test "leaves a tag without v prefix untouched" {
+    write_manifest
+    run "$SCRIPTS_DIR/bump-package-json.sh" "$MANIFEST" "2.0.0"
+    [ "$status" -eq 0 ]
+    [ "$(node -p "require('$MANIFEST').version")" = "2.0.0" ]
+}
+
+@test "handles semver with pre-release suffix" {
+    write_manifest
+    run "$SCRIPTS_DIR/bump-package-json.sh" "$MANIFEST" "v1.0.0-rc.1"
+    [ "$status" -eq 0 ]
+    [ "$(node -p "require('$MANIFEST').version")" = "1.0.0-rc.1" ]
+}
+
+@test "changes only the version line" {
+    write_manifest
+    cp "$MANIFEST" "$TMP_WORKSPACE/before.json"
+
+    run "$SCRIPTS_DIR/bump-package-json.sh" "$MANIFEST" "v1.2.3"
+    [ "$status" -eq 0 ]
+
+    run diff "$TMP_WORKSPACE/before.json" "$MANIFEST"
+    # One changed line: a single `<` and a single `>` in the diff output.
+    [ "$(printf '%s\n' "$output" | grep -c '^<')" -eq 1 ]
+    [ "$(printf '%s\n' "$output" | grep -c '^>')" -eq 1 ]
+    printf '%s\n' "$output" | grep -q '"version": "1.2.3"'
+}
+
+@test "preserves other fields and key order" {
+    write_manifest
+    run "$SCRIPTS_DIR/bump-package-json.sh" "$MANIFEST" "v1.2.3"
+    [ "$status" -eq 0 ]
+    [ "$(node -p "Object.keys(require('$MANIFEST')).join(',')")" = "name,version,scripts" ]
+    [ "$(node -p "require('$MANIFEST').scripts.build")" = "tsc" ]
+}
+
+@test "ignores a nested version field" {
+    cat > "$MANIFEST" << 'JSON'
+{
+    "engines": {
+        "version": "18"
+    },
+    "version": "0.1.0"
+}
+JSON
+    run "$SCRIPTS_DIR/bump-package-json.sh" "$MANIFEST" "v1.2.3"
+    [ "$status" -eq 0 ]
+    [ "$(node -p "require('$MANIFEST').engines.version")" = "18" ]
+    [ "$(node -p "require('$MANIFEST').version")" = "1.2.3" ]
+}
+
+@test "adds a version field when the manifest has none" {
+    printf '{\n  "name": "example"\n}\n' > "$MANIFEST"
+    run "$SCRIPTS_DIR/bump-package-json.sh" "$MANIFEST" "v1.2.3"
+    [ "$status" -eq 0 ]
+    [ "$(node -p "require('$MANIFEST').version")" = "1.2.3" ]
+    [ "$(node -p "require('$MANIFEST').name")" = "example" ]
+}
+
+@test "preserves tab indentation" {
+    printf '{\n\t"name": "example",\n\t"version": "0.1.0"\n}\n' > "$MANIFEST"
+    run "$SCRIPTS_DIR/bump-package-json.sh" "$MANIFEST" "v1.2.3"
+    [ "$status" -eq 0 ]
+    grep -q "$(printf '\t"version": "1.2.3"')" "$MANIFEST"
+}
+
+@test "fails when manifest path is empty" {
+    run "$SCRIPTS_DIR/bump-package-json.sh" "" "v1.0.0"
+    [ "$status" -ne 0 ]
+}
+
+@test "fails when tag is empty" {
+    write_manifest
+    run "$SCRIPTS_DIR/bump-package-json.sh" "$MANIFEST" ""
+    [ "$status" -ne 0 ]
+}
+
+@test "fails when the manifest does not exist" {
+    run "$SCRIPTS_DIR/bump-package-json.sh" "$TMP_WORKSPACE/missing.json" "v1.0.0"
+    [ "$status" -ne 0 ]
+}
+
+@test "fails when the manifest is not valid JSON" {
+    printf 'not json' > "$MANIFEST"
+    run "$SCRIPTS_DIR/bump-package-json.sh" "$MANIFEST" "v1.0.0"
+    [ "$status" -ne 0 ]
+}