affaan-m/ECC · error

MCP config must be a JSON object

Error message

MCP config must be a JSON object

What it means

filterMcpConfig filters disabled MCP servers out of a parsed mcp config. It requires the config to be a plain JSON object; null, arrays, and primitives cannot carry an mcpServers mapping and are rejected before any filtering occurs.

Solutions

1. Pass the parsed JSON object, e.g. JSON.parse(fs.readFileSync(path,'utf8')).
2. Fix the config file so its top level is an object, not an array.
3. Check for a null/undefined return from an earlier load step before filtering.

Example fix

// before
filterMcpConfig(rawConfigText, ['legacy'])
// after
const parsed = JSON.parse(rawConfigText)
filterMcpConfig(parsed, ['legacy'])

let parsed
try { parsed = typeof cfg === 'string' ? JSON.parse(cfg) : cfg } catch { throw new Error('Config is not valid JSON') }
if (parsed === null || typeof parsed !== 'object' || Array.isArray(parsed)) throw new Error('MCP config must be a JSON object')

function isJsonObject(x) {
  return x !== null && typeof x === 'object' && !Array.isArray(x)
}
if (!isJsonObject(config)) throw new TypeError('Expected a JSON object for MCP config')

try {
  const filtered = filterMcpConfig(config, disabled)
} catch (err) {
  if (err.message === 'MCP config must be a JSON object') {
    console.error('Config must be a parsed JSON object with an mcpServers key')
  } else throw err
}

When it happens

Trigger: Calling filterMcpConfig(null), filterMcpConfig([]), filterMcpConfig('...'), or passing a parsed JSON file whose top level is an array instead of an object.

Common situations: An mcp-configs file saved as a JSON array of configs; a failed read yielding null passed straight through; passing the raw file text string instead of JSON.parse output.

Understand the failure class

Background: "Invalid value" and "allowed values are" config errors: what your library rejected and how to fix it — this error's family across 41 libraries.

Related errors

• -32602
• A normalized install request is required
• application request must be a JSON object
• bundle collections must be lists
• bundle values must be finite JSON data

AI-assisted analysis of affaan-m/ECC@8321021c54 (2026-09-16). Data as JSON: /api/errors/559543d91d353d3e. Report an issue: GitHub.

Appendix: source

Thrown at scripts/lib/mcp-config.js:14

'use strict';

function parseDisabledMcpServers(value) {
  return [...new Set(
    String(value || '')
      .split(',')
      .map((entry) => entry.trim())
      .filter(Boolean)
  )];
}

function filterMcpConfig(config, disabledServerNames = []) {
  if (!config || typeof config !== 'object' || Array.isArray(config)) {
    throw new Error('MCP config must be a JSON object');
  }

  const servers = config.mcpServers;
  if (!servers || typeof servers !== 'object' || Array.isArray(servers)) {
    throw new Error('MCP config must include an mcpServers object');
  }

  const disabled = new Set(parseDisabledMcpServers(disabledServerNames));
  if (disabled.size === 0) {
    return {
      config: {
        ...config,
        mcpServers: { ...servers },
      },
      removed: [],
    };
  }

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