---
title: "Model Context Protocol (MCP) Error Decoder"
canonical: "https://mcp-codex.com/errors"
source: "MCP Codex (https://mcp-codex.com)"
count: 9
dateModified: "2026-09-28"
---

# MCP Error Decoder & Diagnostics (9 Known Errors)

Verified symptoms, root causes, and remediation fixes for common Model Context Protocol (MCP) runtime errors.

| Code | Title | Category | Severity | Markdown Doc |
| :--- | :--- | :--- | :--- | :--- |
| `ENOENT` | [spawn npx ENOENT / command not found](https://mcp-codex.com/errors/spawn-npx-enoent) | Environment & Runtime | Critical | [spawn-npx-enoent.md](https://mcp-codex.com/errors/spawn-npx-enoent.md) |
| `-32603` | [JSON-RPC error -32603: Internal error (STDOUT Pollution)](https://mcp-codex.com/errors/json-rpc-32603-internal-error) | Protocol & Serialization | High | [json-rpc-32603-internal-error.md](https://mcp-codex.com/errors/json-rpc-32603-internal-error.md) |
| `-32602` | [JSON-RPC error -32602: Invalid params](https://mcp-codex.com/errors/json-rpc-32602-invalid-params) | Protocol & Serialization | Medium | [json-rpc-32602-invalid-params.md](https://mcp-codex.com/errors/json-rpc-32602-invalid-params.md) |
| `-32700` | [JSON-RPC error -32700: Parse error / Invalid Windows backslashes](https://mcp-codex.com/errors/windows-backslash-json-parse-error) | Configuration Syntax | High | [windows-backslash-json-parse-error.md](https://mcp-codex.com/errors/windows-backslash-json-parse-error.md) |
| `SSE_CLOSED` | [SSE connection closed prematurely / EOF](https://mcp-codex.com/errors/sse-connection-closed) | Network & Transport | High | [sse-connection-closed.md](https://mcp-codex.com/errors/sse-connection-closed.md) |
| `HTTP 403` | [GitHub MCP 403: Resource protected by organization SAML](https://mcp-codex.com/errors/github-403-saml-sso) | Authentication | Medium | [github-403-saml-sso.md](https://mcp-codex.com/errors/github-403-saml-sso.md) |
| `TIMEOUT` | [Tool call timed out after 60000ms](https://mcp-codex.com/errors/tool-call-timeout-60s) | Performance & Database | Medium | [tool-call-timeout-60s.md](https://mcp-codex.com/errors/tool-call-timeout-60s.md) |
| `SSL_ERR` | [PostgreSQL: no pg_hba.conf entry for host / SSL required](https://mcp-codex.com/errors/postgres-ssl-required) | Database Integration | High | [postgres-ssl-required.md](https://mcp-codex.com/errors/postgres-ssl-required.md) |
| `EACCES` | [Filesystem MCP: Permission Denied / Outside Root Sandbox](https://mcp-codex.com/errors/filesystem-permission-denied-eacces) | Security & Sandbox | High | [filesystem-permission-denied-eacces.md](https://mcp-codex.com/errors/filesystem-permission-denied-eacces.md) |

## Machine Readable Endpoint
- Agent API: https://mcp-codex.com/api/agent/errors
- Weekly Protocol Changelog: https://mcp-codex.com#newsletter