oraios/serena · error · FileNotFoundError

vscode-json-languageserver executable not found at {json_exe

Error message

vscode-json-languageserver executable not found at {json_executable_path}, something went wrong with the installation.

What it means

The JSON language server is installed via npm (vscode-json-languageserver) into json_ls_dir, but after running deps.install the expected executable still cannot be found, so _get_or_install_core_dependency raises FileNotFoundError indicating the installation did not produce the expected artifact.

Source

Thrown at src/solidlsp/language_servers/json_language_server.py:92

            # legacy unversioned dir reserved for INITIAL; every other version goes into a versioned subdir
            ls_dirname = (
                "json-lsp"
                if json_language_server_version == INITIAL_JSON_LANGUAGE_SERVER_VERSION
                else f"json-lsp-{json_language_server_version}"
            )
            json_ls_dir = os.path.join(self._ls_resources_dir, ls_dirname)
            json_executable_path = os.path.join(json_ls_dir, "node_modules", ".bin", "vscode-json-languageserver")

            if os.name == "nt":
                json_executable_path += ".cmd"

            if not os.path.exists(json_executable_path):
                log.info(f"JSON Language Server executable not found at {json_executable_path}. Installing...")
                deps.install(json_ls_dir)
                log.info("JSON language server dependencies installed successfully")

            if not os.path.exists(json_executable_path):
                raise FileNotFoundError(
                    f"vscode-json-languageserver executable not found at {json_executable_path}, something went wrong with the installation."
                )

            return json_executable_path

        def _create_launch_command(self, core_path: str) -> list[str]:
            return [core_path, "--stdio"]

    def _create_base_initialize_params(self) -> dict:
        """
        Returns the initialize params for the JSON Language Server.
        """
        initialize_params = {
            "locale": "en",
            "capabilities": {
                "textDocument": {
                    "synchronization": {"didSave": True, "dynamicRegistration": True},

View on GitHub (pinned to 7fcbca7e62)

Solutions

1. Run the install manually inside json_ls_dir (`npm install`) and check npm's stderr for real errors.
2. Verify the actual executable location (e.g. json_ls_dir/node_modules/.bin/vscode-json-languageserver) and correct json_executable_path resolution if the package layout changed.
3. Ensure node/npm are installed and on PATH, then delete json_ls_dir and let Serena reinstall fresh.
4. Check disk space and directory write permissions for json_ls_dir.

Example fix

// before (npm not on PATH, silent failure)
# serena start --language json
// FileNotFoundError: vscode-json-languageserver executable not found...
// after
$ which npm && npm -v
$ cd <json_ls_dir> && npm install
$ ls node_modules/.bin/vscode-json-languageserver

import shutil, os
def validate_json_ls_installable(json_ls_dir: str, executable_path: str) -> bool:
    if shutil.which("npm") is None:
        return False
    if not os.access(json_ls_dir, os.W_OK):
        return False
    return True  # then run `npm install` in json_ls_dir and check node_modules/.bin/vscode-json-languageserver

try:
    json_path = get_or_install_core_dependency()
except FileNotFoundError as e:
    if "vscode-json-languageserver" in str(e):
        subprocess.run(["npm", "install"], cwd=json_ls_dir, check=True)  # surface npm's real error
        bin_path = os.path.join(json_ls_dir, "node_modules", ".bin", "vscode-json-languageserver")
        if not os.path.exists(bin_path):
            raise RuntimeError("npm install produced no vscode-json-languageserver binary") from e
    else:
        raise

When it happens

Trigger: _get_or_install_core_dependency: json_executable_path does not exist, deps.install(json_ls_dir) runs npm install, but a second os.path.exists(json_executable_path) still fails, raising the error.

Common situations: npm not installed or failing (network/registry errors swallowed); npm installed to a different global/node_modules layout so the binary path differs (e.g. node_modules/.bin/vscode-json-languageserver missing); Node version incompatibility with the package; antivirus or permissions blocking binary creation.

Related errors

• shader-language-server not found at {executable_path}
• typescript-language-server executable not found at {tsserver
• {LS_BIN_NAME} executable not found at {executable_path}; npm
• vue-language-server executable not found at {vue_executable_
• typescript-language-server executable not found at {ts_ls_ex

AI-assisted analysis of oraios/serena@7fcbca7e62 (2026-08-29). Data as JSON: /api/errors/0a8baf7255f5041c. Report an issue: GitHub.