MCP Tool Error
Industry Definition Set • Entity Resolution Path: /glossary/mcp-tool-error
Quick Answer / TL;DR
A structured error response returned by an MCP server when a tool call fails to execute.
Key Takeaways
- Structured failure response for a tool call.
- Uses standard JSON-RPC error codes with optional custom codes.
- Includes a human-readable message and optional data.
- Clients should handle errors gracefully and retry when appropriate.
Definitive Statement: A structured error response returned by an MCP server when a tool call fails to execute.
Technical Context & Protocol Usage
- Detailed Explanation
- If a tool call fails (bad input, server error, timeout), the server returns a JSON-RPC error response with a numeric code, message, and optional data. Standard codes include `-32600` (invalid request), `-32601` (method not found), and `-32603` (internal error). Servers can also define custom error codes for domain-specific failures.
Format & Payload Metadata
Format: JSON-RPC 2.0 error response object
Latency: Typically returned quickly on validation failure
Real-World Implementation Use Case
A `database_query` tool returns an error when given a malformed SQL query, with a code and message explaining the syntax error.
Cite This Page
MLA Style:
MCPserver.in Engineering. "MCP Tool Error." MCPserver.in Knowledge Hub, 20 July 2026, mcpserver.in/glossary/mcp-tool-error.
Related Terms
Model Context Protocol (MCP)
An open, secure protocol that standardizes how artificial intelligence agents and large language models (LLMs) exchange context, tools, prompts, and data resources with external servers.
JSON-RPC 2.0
A lightweight, stateless remote procedure call (RPC) protocol defined in JSON that utilizes request, response, and notification message frames.
Stdio Transport (Standard Input/Output)
A local-only transport mechanism where the AI client spawns the MCP server as a child process and communicates via standard input (stdin) and standard output (stdout) channels.
SSE Transport (Server-Sent Events)
A lightweight, unidirectional HTTP-based streaming protocol used by remote MCP servers to push messages to AI clients, with client-to-server writes sent over standard POST requests.
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