langchain-ai/deepagents · error · PluginManifestError

Plugin manifest {manifest_path} must be a JSON object

Error message

Plugin manifest {manifest_path} must be a JSON object

What it means

After successfully parsing the manifest JSON, `load_manifest` requires the decoded value to be a JSON object (dict). If the file parses but contains a list, string, number, or `null`, this `PluginManifestError` is raised — the manifest schema is object-shaped (`name`, `version`, component path fields).

Source

Thrown at libs/code/deepagents_code/plugins/manifest.py:284

        `(manifest, manifest_path, warnings)`.

    Raises:
        PluginManifestError: If the manifest exists but is invalid.
    """
    manifest_path = find_manifest_path(root)
    if manifest_path is None:
        return None, None, ()
    try:
        decoded = json.loads(manifest_path.read_text(encoding="utf-8"))
    except json.JSONDecodeError as exc:
        msg = f"Invalid JSON syntax in {manifest_path}: {exc}"
        raise PluginManifestError(msg) from exc
    except OSError as exc:
        msg = f"Could not read plugin manifest {manifest_path}: {exc}"
        raise PluginManifestError(msg) from exc
    if not isinstance(decoded, dict):
        msg = f"Plugin manifest {manifest_path} must be a JSON object"
        raise PluginManifestError(msg)
    raw = json_object(decoded)

    warnings: list[str] = []
    name = _validate_name(raw.get("name"), fallback=fallback_name)
    component_paths: dict[str, tuple[Path, ...]] = {}
    for field_name in _PATH_COMPONENT_FIELDS:
        declaration = raw.get(field_name)
        if declaration is None:
            continue
        if field_name in {"mcpServers", "hooks"} and isinstance(declaration, dict):
            continue
        paths = _resolve_component_paths(declaration, root, field_name, warnings)
        if paths:
            component_paths[field_name] = paths

    version_value = raw.get("version")
    version = version_value if isinstance(version_value, str) else None
    display_name_value = raw.get("displayName")

View on GitHub (pinned to a1af029e6e)

Solutions

1. Reshape the manifest to a top-level JSON object with fields like `name`, `version`, and component paths.
2. If it's a list of manifests, split into one object per plugin directory.
3. Validate with `python -c "import json,sys; d=json.load(open('plugin.json')); assert isinstance(d, dict)"` before publishing.

Example fix

// before
[{"name": "x", "version": "1.0"}]
// after
{"name": "x", "version": "1.0"}

import json
from pathlib import Path
d = json.loads(Path("plugin.json").read_text(encoding="utf-8"))
assert isinstance(d, dict), "manifest must be a JSON object, not a list/string"

def is_manifest_object(decoded: object) -> bool:
    return isinstance(decoded, dict)

try:
    manifest, _, _ = load_manifest(root)
except PluginManifestError as exc:
    if "must be a JSON object" in str(exc):
        print(f"reshape manifest to a top-level object: {exc}")

When it happens

Trigger: `load_manifest` is called on a plugin root whose manifest file contains valid JSON that is not an object — e.g. a top-level array, a bare quoted string, or `null`.

Common situations: Author wrapped the manifest in an array `[ {...} ]`; file accidentally contains only a version string; a generator/export tool emitted a JSON list of manifests instead of one object.

Related errors

• Invalid JSON syntax in {manifest_path}: {exc}
• External event must be a JSON object
• External event kind must be one of {sorted(_VALID_KINDS)}; g
• Invalid plugin name: {name!r}
• Could not read plugin manifest {manifest_path}: {exc}

AI-assisted analysis of langchain-ai/deepagents@a1af029e6e (2026-08-29). Data as JSON: /api/errors/becd909007e7911c. Report an issue: GitHub.