diff --git a/AGENTS.md b/AGENTS.md
index 287504a..0d206d7 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -237,3 +237,11 @@ jobs:
       - name: Run tests
         run: bash run_test.sh
 ```
+
+## Zusaetzliche Runner-Guidelines (framework-agnostisch)
+
+- **Testnamen-Konvention:** Runner sollen eine konsistente, dokumentierte Full-Name-Bildung verwenden (z. B. `Parent/Subtest`), inklusive Mehrfach-Nesting. Diese Konvention muss in `results.*`, `parse_test_output` und `collect_failed_locations` uebereinstimmen.
+- **TSamNearest-Prioritaet:** Falls moeglich, gelten folgende Regeln: Test-Block > Describe/Context-Block > File-Command. Das Verhalten muss getestet werden (Cursor im Test, zwischen Tests, ausserhalb von Describe/Context).
+- **Reporter-Payload-Schema:** Wenn ein Custom-Reporter verwendet wird, soll dessen JSON-Payload dokumentiert und stabil sein (z. B. `{ name, status, file, location, output }`), damit Parser/Quickfix/Detail-Output konsistent bleiben.
+- **Failed-Only-Logik:** Failed-Only muss auf den letzten Fehlermeldungen basieren und nur die fehlerhaften Tests erneut ausfuehren. Die Pattern-Strategie (z. B. Titel-only vs. Full-Name) muss getestet werden.
+- **CI-Installations-Snippet:** Die Neovim-Installation in CI soll als „authoritative snippet“ behandelt werden und in Runner-Repos 1:1 uebernommen werden.
diff --git a/README.md b/README.md
index 5981fcc..81d27cc 100644
--- a/README.md
+++ b/README.md
@@ -7,6 +7,7 @@ Main plugin: https://gitea.mschirmer.com/m13r/test-samurai.nvim
 ## Features
 
 - Detects Jest test files (`*.test.*`, `*.spec.*`).
+- Activates only when the nearest `package.json` lists `jest` in dependencies or devDependencies.
 - Finds nearest `test`/`it` within `describe` blocks.
 - Builds `npx jest` commands for nearest, file, all, and failed-only runs.
 - Streams results via a custom Jest reporter using `onTestCaseResult`.
diff --git a/lua/test-samurai-jest-runner/init.lua b/lua/test-samurai-jest-runner/init.lua
index a7e8a00..5aec668 100644
--- a/lua/test-samurai-jest-runner/init.lua
+++ b/lua/test-samurai-jest-runner/init.lua
@@ -38,6 +38,47 @@ local function find_root(path, markers)
   return vim.fs.dirname(found[1])
 end
 
+local function find_nearest_package_root(path)
+  if not path or path == "" then
+    return nil
+  end
+  local dir = vim.fs.dirname(path)
+  local prev = nil
+  while dir and dir ~= prev do
+    local candidate = dir .. "/package.json"
+    if vim.fn.filereadable(candidate) == 1 then
+      return dir
+    end
+    prev = dir
+    dir = vim.fs.dirname(dir)
+  end
+  return nil
+end
+
+local function read_package_json(root)
+  if not root then
+    return nil
+  end
+  local ok, lines = pcall(vim.fn.readfile, root .. "/package.json")
+  if not ok then
+    return nil
+  end
+  local ok_decode, data = pcall(vim.json.decode, table.concat(lines, "\n"))
+  if not ok_decode then
+    return nil
+  end
+  return data
+end
+
+local function has_jest_dependency(pkg)
+  if not pkg or type(pkg) ~= "table" then
+    return false
+  end
+  local deps = pkg.dependencies or {}
+  local dev_deps = pkg.devDependencies or {}
+  return deps.jest ~= nil or dev_deps.jest ~= nil
+end
+
 local function count_char(line, ch)
   local count = 0
   for i = 1, #line do
@@ -346,7 +387,12 @@ end
 
 function runner.is_test_file(bufnr)
   local path = get_buf_path(bufnr)
-  return test_file_path(path)
+  if not test_file_path(path) then
+    return false
+  end
+  local root = find_nearest_package_root(path)
+  local pkg = read_package_json(root)
+  return has_jest_dependency(pkg)
 end
 
 function runner.find_nearest(bufnr, row, _col)
@@ -354,7 +400,7 @@ function runner.find_nearest(bufnr, row, _col)
   if not path or path == "" then
     return nil, "no file name"
   end
-  if not test_file_path(path) then
+  if not runner.is_test_file(bufnr) then
     return nil, "not a jest test file"
   end
   local lines = get_buf_lines(bufnr)
diff --git a/tests/test_jest_runner_spec.lua b/tests/test_jest_runner_spec.lua
index a401022..7882943 100644
--- a/tests/test_jest_runner_spec.lua
+++ b/tests/test_jest_runner_spec.lua
@@ -1,5 +1,37 @@
 local runner = require("test-samurai-jest-runner")
 
+local function write_file(path, content)
+  local dir = vim.fn.fnamemodify(path, ":h")
+  vim.fn.mkdir(dir, "p")
+  vim.fn.writefile(vim.split(content, "\n"), path)
+end
+
+local function with_project(package_json, fn)
+  local root = vim.fn.tempname()
+  vim.fn.mkdir(root, "p")
+  root = vim.loop.fs_realpath(root) or root
+  if package_json then
+    write_file(root .. "/package.json", package_json)
+  end
+  fn(root)
+end
+
+local JEST_PACKAGE = [[
+{
+  "devDependencies": {
+    "jest": "^29.0.0"
+  }
+}
+]]
+
+local NO_JEST_PACKAGE = [[
+{
+  "devDependencies": {
+    "mocha": "^10.0.0"
+  }
+}
+]]
+
 local function get_reporter_path()
   local source = debug.getinfo(runner.build_command, "S").source
   if source:sub(1, 1) == "@" then
@@ -10,157 +42,147 @@ local function get_reporter_path()
 end
 
 describe("test-samurai-jest-runner", function()
-  it("detects Jest test files by suffix", function()
-    local bufnr1 = vim.api.nvim_create_buf(false, true)
-    vim.api.nvim_buf_set_name(bufnr1, "/tmp/example.test.js")
-    assert.is_true(runner.is_test_file(bufnr1))
+  it("detects Jest test files by suffix and package.json", function()
+    with_project(JEST_PACKAGE, function(root)
+      local bufnr1 = vim.api.nvim_create_buf(false, true)
+      vim.api.nvim_buf_set_name(bufnr1, root .. "/example.test.js")
+      assert.is_true(runner.is_test_file(bufnr1))
 
-    local bufnr2 = vim.api.nvim_create_buf(false, true)
-    vim.api.nvim_buf_set_name(bufnr2, "/tmp/example.spec.tsx")
-    assert.is_true(runner.is_test_file(bufnr2))
+      local bufnr2 = vim.api.nvim_create_buf(false, true)
+      vim.api.nvim_buf_set_name(bufnr2, root .. "/example.spec.tsx")
+      assert.is_true(runner.is_test_file(bufnr2))
 
-    local bufnr3 = vim.api.nvim_create_buf(false, true)
-    vim.api.nvim_buf_set_name(bufnr3, "/tmp/example.js")
-    assert.is_false(runner.is_test_file(bufnr3))
+      local bufnr3 = vim.api.nvim_create_buf(false, true)
+      vim.api.nvim_buf_set_name(bufnr3, root .. "/example.js")
+      assert.is_false(runner.is_test_file(bufnr3))
+    end)
+  end)
+
+  it("rejects test files when jest dependency is missing", function()
+    with_project(NO_JEST_PACKAGE, function(root)
+      local bufnr = vim.api.nvim_create_buf(false, true)
+      vim.api.nvim_buf_set_name(bufnr, root .. "/example.test.js")
+      assert.is_false(runner.is_test_file(bufnr))
+    end)
   end)
 
   it("finds nearest test with describe hierarchy", function()
-    local bufnr = vim.api.nvim_create_buf(false, true)
-    vim.api.nvim_buf_set_name(bufnr, "/tmp/math.test.js")
-    local lines = {
-      "describe('Math', () => {",
-      "  test('adds', () => {",
-      "    expect(1 + 1).toBe(2)",
-      "  })",
-      "})",
-    }
-    vim.api.nvim_buf_set_lines(bufnr, 0, -1, false, lines)
+    with_project(JEST_PACKAGE, function(root)
+      local bufnr = vim.api.nvim_create_buf(false, true)
+      vim.api.nvim_buf_set_name(bufnr, root .. "/math.test.js")
+      local lines = {
+        "describe('Math', () => {",
+        "  test('adds', () => {",
+        "    expect(1 + 1).toBe(2)",
+        "  })",
+        "})",
+      }
+      vim.api.nvim_buf_set_lines(bufnr, 0, -1, false, lines)
 
-    local orig_fs_find = vim.fs.find
-    vim.fs.find = function(_, _)
-      return { "/tmp/package.json" }
-    end
+      local spec, err = runner.find_nearest(bufnr, 2, 0)
 
-    local spec, err = runner.find_nearest(bufnr, 2, 0)
-
-    vim.fs.find = orig_fs_find
-
-    assert.is_nil(err)
-    assert.equals("adds", spec.test_name)
-    assert.equals("Math/adds", spec.full_name)
-    assert.equals("Math adds", spec.jest_name)
-    assert.are.same({ "Math", "adds" }, spec.jest_parts)
-    assert.is_true(spec.file:match("math%.test%.js$") ~= nil)
-    assert.equals("/tmp", spec.cwd)
+      assert.is_nil(err)
+      assert.equals("adds", spec.test_name)
+      assert.equals("Math/adds", spec.full_name)
+      assert.equals("Math adds", spec.jest_name)
+      assert.are.same({ "Math", "adds" }, spec.jest_parts)
+      assert.is_true(spec.file:match("math%.test%.js$") ~= nil)
+      assert.equals(root, spec.cwd)
+    end)
   end)
 
   it("handles multiline describe and it declarations", function()
-    local bufnr = vim.api.nvim_create_buf(false, true)
-    vim.api.nvim_buf_set_name(bufnr, "/tmp/multiline.test.js")
-    local lines = {
-      "describe(",
-      "  '<Header/>',",
-      "  () => {",
-      "    describe(",
-      "      'renders properly...',",
-      "      () => {",
-      "        it(",
-      "          'the teaser links',",
-      "          async () => {",
-      "            expect(true).toBe(true)",
-      "          }",
-      "        )",
-      "      }",
-      "    )",
-      "  }",
-      ")",
-    }
-    vim.api.nvim_buf_set_lines(bufnr, 0, -1, false, lines)
+    with_project(JEST_PACKAGE, function(root)
+      local bufnr = vim.api.nvim_create_buf(false, true)
+      vim.api.nvim_buf_set_name(bufnr, root .. "/multiline.test.js")
+      local lines = {
+        "describe(",
+        "  '<Header/>',",
+        "  () => {",
+        "    describe(",
+        "      'renders properly...',",
+        "      () => {",
+        "        it(",
+        "          'the teaser links',",
+        "          async () => {",
+        "            expect(true).toBe(true)",
+        "          }",
+        "        )",
+        "      }",
+        "    )",
+        "  }",
+        ")",
+      }
+      vim.api.nvim_buf_set_lines(bufnr, 0, -1, false, lines)
 
-    local orig_fs_find = vim.fs.find
-    vim.fs.find = function(_, _)
-      return { "/tmp/package.json" }
-    end
+      local spec, err = runner.find_nearest(bufnr, 9, 0)
 
-    local spec, err = runner.find_nearest(bufnr, 9, 0)
-
-    vim.fs.find = orig_fs_find
-
-    assert.is_nil(err)
-    assert.equals("the teaser links", spec.test_name)
-    assert.equals("<Header/>/renders properly.../the teaser links", spec.full_name)
-    assert.are.same({ "<Header/>", "renders properly...", "the teaser links" }, spec.jest_parts)
+      assert.is_nil(err)
+      assert.equals("the teaser links", spec.test_name)
+      assert.equals("<Header/>/renders properly.../the teaser links", spec.full_name)
+      assert.are.same({ "<Header/>", "renders properly...", "the teaser links" }, spec.jest_parts)
+    end)
   end)
 
   it("uses describe block when cursor is between tests", function()
-    local bufnr = vim.api.nvim_create_buf(false, true)
-    vim.api.nvim_buf_set_name(bufnr, "/tmp/between.test.js")
-    local lines = {
-      "describe('<Header/>', () => {",
-      "  describe('renders properly...', () => {",
-      "    it('the logo', async () => {",
-      "      expect(true).toBe(true)",
-      "    })",
-      "    ",
-      "    it('the teaser links', async () => {",
-      "      expect(true).toBe(true)",
-      "    })",
-      "  })",
-      "})",
-    }
-    vim.api.nvim_buf_set_lines(bufnr, 0, -1, false, lines)
+    with_project(JEST_PACKAGE, function(root)
+      local bufnr = vim.api.nvim_create_buf(false, true)
+      vim.api.nvim_buf_set_name(bufnr, root .. "/between.test.js")
+      local lines = {
+        "describe('<Header/>', () => {",
+        "  describe('renders properly...', () => {",
+        "    it('the logo', async () => {",
+        "      expect(true).toBe(true)",
+        "    })",
+        "    ",
+        "    it('the teaser links', async () => {",
+        "      expect(true).toBe(true)",
+        "    })",
+        "  })",
+        "})",
+      }
+      vim.api.nvim_buf_set_lines(bufnr, 0, -1, false, lines)
 
-    local orig_fs_find = vim.fs.find
-    vim.fs.find = function(_, _)
-      return { "/tmp/package.json" }
-    end
+      local spec, err = runner.find_nearest(bufnr, 5, 0)
 
-    local spec, err = runner.find_nearest(bufnr, 5, 0)
-
-    vim.fs.find = orig_fs_find
-
-    assert.is_nil(err)
-    assert.equals("renders properly...", spec.test_name)
-    assert.equals("<Header/>/renders properly...", spec.full_name)
-    assert.are.same({ "<Header/>", "renders properly..." }, spec.jest_parts)
-    assert.equals("describe", spec.kind)
+      assert.is_nil(err)
+      assert.equals("renders properly...", spec.test_name)
+      assert.equals("<Header/>/renders properly...", spec.full_name)
+      assert.are.same({ "<Header/>", "renders properly..." }, spec.jest_parts)
+      assert.equals("describe", spec.kind)
+    end)
   end)
 
   it("falls back to file command when outside any describe", function()
-    local bufnr = vim.api.nvim_create_buf(false, true)
-    vim.api.nvim_buf_set_name(bufnr, "/tmp/outside.test.js")
-    local lines = {
-      "const value = 1",
-      "function helper() { return value }",
-    }
-    vim.api.nvim_buf_set_lines(bufnr, 0, -1, false, lines)
+    with_project(JEST_PACKAGE, function(root)
+      local bufnr = vim.api.nvim_create_buf(false, true)
+      vim.api.nvim_buf_set_name(bufnr, root .. "/outside.test.js")
+      local lines = {
+        "const value = 1",
+        "function helper() { return value }",
+      }
+      vim.api.nvim_buf_set_lines(bufnr, 0, -1, false, lines)
 
-    local orig_fs_find = vim.fs.find
-    vim.fs.find = function(_, _)
-      return { "/tmp/package.json" }
-    end
+      local spec, err = runner.find_nearest(bufnr, 1, 0)
+      assert.is_nil(err)
+      assert.equals("file", spec.kind)
 
-    local spec, err = runner.find_nearest(bufnr, 1, 0)
-    assert.is_nil(err)
-    assert.equals("file", spec.kind)
+      local cmd_spec = runner.build_command(spec)
 
-    local cmd_spec = runner.build_command(spec)
-
-    vim.fs.find = orig_fs_find
-
-    assert.are.same(
-      {
-        "npx",
-        "jest",
-        "--testLocationInResults",
-        "--reporters",
-        get_reporter_path(),
-        "--runTestsByPath",
-        cmd_spec.cmd[#cmd_spec.cmd],
-      },
-      cmd_spec.cmd
-    )
-    assert.is_true(cmd_spec.cmd[#cmd_spec.cmd]:match("outside%.test%.js$") ~= nil)
+      assert.are.same(
+        {
+          "npx",
+          "jest",
+          "--testLocationInResults",
+          "--reporters",
+          get_reporter_path(),
+          "--runTestsByPath",
+          cmd_spec.cmd[#cmd_spec.cmd],
+        },
+        cmd_spec.cmd
+      )
+      assert.is_true(cmd_spec.cmd[#cmd_spec.cmd]:match("outside%.test%.js$") ~= nil)
+    end)
   end)
 
   it("build_command uses npx jest with reporter and pattern", function()
@@ -218,57 +240,47 @@ describe("test-samurai-jest-runner", function()
   end)
 
   it("build_file_command scopes to file", function()
-    local bufnr = vim.api.nvim_create_buf(false, true)
-    vim.api.nvim_buf_set_name(bufnr, "/tmp/project/foo.test.ts")
+    with_project(JEST_PACKAGE, function(root)
+      local bufnr = vim.api.nvim_create_buf(false, true)
+      vim.api.nvim_buf_set_name(bufnr, root .. "/foo.test.ts")
 
-    local orig_fs_find = vim.fs.find
-    vim.fs.find = function(_, _)
-      return { "/tmp/project/package.json" }
-    end
+      local cmd_spec = runner.build_file_command(bufnr)
 
-    local cmd_spec = runner.build_file_command(bufnr)
-
-    vim.fs.find = orig_fs_find
-
-    assert.are.same(
-      {
-        "npx",
-        "jest",
-        "--testLocationInResults",
-        "--reporters",
-        get_reporter_path(),
-        "--runTestsByPath",
-        "/tmp/project/foo.test.ts",
-      },
-      cmd_spec.cmd
-    )
-    assert.equals("/tmp/project", cmd_spec.cwd)
+      assert.are.same(
+        {
+          "npx",
+          "jest",
+          "--testLocationInResults",
+          "--reporters",
+          get_reporter_path(),
+          "--runTestsByPath",
+          root .. "/foo.test.ts",
+        },
+        cmd_spec.cmd
+      )
+      assert.equals(root, cmd_spec.cwd)
+    end)
   end)
 
   it("build_all_command runs project tests", function()
-    local bufnr = vim.api.nvim_create_buf(false, true)
-    vim.api.nvim_buf_set_name(bufnr, "/tmp/project/bar.test.ts")
+    with_project(JEST_PACKAGE, function(root)
+      local bufnr = vim.api.nvim_create_buf(false, true)
+      vim.api.nvim_buf_set_name(bufnr, root .. "/bar.test.ts")
 
-    local orig_fs_find = vim.fs.find
-    vim.fs.find = function(_, _)
-      return { "/tmp/project/package.json" }
-    end
+      local cmd_spec = runner.build_all_command(bufnr)
 
-    local cmd_spec = runner.build_all_command(bufnr)
-
-    vim.fs.find = orig_fs_find
-
-    assert.are.same(
-      {
-        "npx",
-        "jest",
-        "--testLocationInResults",
-        "--reporters",
-        get_reporter_path(),
-      },
-      cmd_spec.cmd
-    )
-    assert.equals("/tmp/project", cmd_spec.cwd)
+      assert.are.same(
+        {
+          "npx",
+          "jest",
+          "--testLocationInResults",
+          "--reporters",
+          get_reporter_path(),
+        },
+        cmd_spec.cmd
+      )
+      assert.equals(root, cmd_spec.cwd)
+    end)
   end)
 
   it("build_failed_command narrows to failed tests", function()