langchain-ai/deepagents · error · MarketplaceError

Invalid JSON syntax in {manifest_path}: {exc}

Error message

Invalid JSON syntax in {manifest_path}: {exc}

What it means

Marketplace manifests (.marketplace.json style files) are parsed with json.loads when loading a marketplace from a path. If the file contains malformed JSON, the underlying json.JSONDecodeError is wrapped in MarketplaceError with the file path and parser detail so callers get a single domain exception type. It is a configuration-content error, not a lookup failure.

Source

Thrown at libs/code/deepagents_code/plugins/marketplace.py:808

    )
    display_name_value = entry.get("displayName")
    return MarketplacePluginEntry(
        name=name,
        source=source,
        description=description_value if isinstance(description_value, str) else None,
        author=author,
        display_name=(
            display_name_value if isinstance(display_name_value, str) else None
        ),
    )


def _load_marketplace_from_path(root: Path, manifest_path: Path) -> PluginMarketplace:
    try:
        raw = json.loads(manifest_path.read_text(encoding="utf-8"))
    except json.JSONDecodeError as exc:
        msg = f"Invalid JSON syntax in {manifest_path}: {exc}"
        raise MarketplaceError(msg) from exc
    except OSError as exc:
        msg = f"Could not read marketplace manifest {manifest_path}: {exc}"
        raise MarketplaceError(msg) from exc
    if not isinstance(raw, dict):
        msg = f"Marketplace manifest {manifest_path} must be a JSON object"
        raise MarketplaceError(msg)
    try:
        name = _validate_name(raw.get("name"), allow_at=False)
    except ValueError as exc:
        raise MarketplaceError(str(exc)) from exc
    plugins_raw = raw.get("plugins")
    if not isinstance(plugins_raw, list):
        msg = f"Marketplace {name} must contain a plugins array"
        raise MarketplaceError(msg)
    warnings: list[str] = []
    plugins = tuple(
        plugin
        for entry in plugins_raw

View on GitHub (pinned to a1af029e6e)

Solutions

1. Open the manifest path printed in the message and fix the JSON syntax at the line/column reported in the exc detail (validate with `python -m json.tool <file>`).
2. Re-clone or re-download the marketplace repository if the file is corrupted or truncated.
3. If the file is generated, regenerate it with a JSON serializer instead of string concatenation; strip BOM/comments.

Example fix

// before (broken manifest)
{ "name": "my-market", "plugins": [ { "id": "a", } ] }   // trailing comma
// after
{ "name": "my-market", "plugins": [ { "id": "a" } ] }

import json
from pathlib import Path

def manifest_is_valid_json(path: Path) -> bool:
    try:
        json.loads(path.read_text(encoding="utf-8-sig"))
        return True
    except (json.JSONDecodeError, OSError):
        return False

def is_json_object(raw: object) -> TypeGuard[dict]:
    return isinstance(raw, dict)

from deepagents_code.plugins import MarketplaceError
try:
    mp = load_marketplace(root)
except MarketplaceError as exc:
    logger.error("Marketplace load failed: %s", exc)
    mp = None

When it happens

Trigger: Calling load_marketplace(root) / _load_marketplace_file / add_local_marketplace where find_marketplace_manifest located a manifest whose bytes are not valid JSON (json.JSONDecodeError branch in _load_marketplace_from_path).

Common situations: Hand-edited marketplace.json with a trailing comma, missing brace, or comments; a truncated download of a marketplace repo; a file saved with BOM or HTML error page content instead of JSON; merge-conflict markers left in the manifest.

Understand the failure class

• Parsing and encoding errors: unexpected token, malformed input — why parsers reject input and how to find the real culprit.

Related errors

• Failed to parse {SERVER_ENV_PREFIX}{suffix} as JSON: {exc}.
• Invalid MCP config at {mcp_config_path}: {exc}
• Marketplace manifest {manifest_path} must be a JSON object
• Invalid plugin name: {name!r}
• Marketplace {name} must contain a plugins array

AI-assisted analysis of langchain-ai/deepagents@a1af029e6e (2026-08-29). Data as JSON: /api/errors/db66a5bdc31032f1. Report an issue: GitHub.