MCP Tool List Changed
Industry Definition Set • Entity Resolution Path: /glossary/mcp-tool-list-changed
Quick Answer / TL;DR
A server-to-client notification that the set of available tools has changed, prompting the client to refresh its cached tool list.
Key Takeaways
- Server-side dynamic tool registry updates.
- Client must re-query tools/list upon receiving this notification.
- Useful for multi-tenant or role-based tool access.
- Part of the standard MCP notification set.
Definitive Statement: A server-to-client notification that the set of available tools has changed, prompting the client to refresh its cached tool list.
Technical Context & Protocol Usage
- Detailed Explanation
- Servers may dynamically add or remove tools at runtime (e.g., when a user authenticates a new data source). The `tools/list_changed` notification tells the client to re-fetch the tool list. Clients must listen for this notification and update their internal tool registry, which may also require re-rendering UI elements.
Format & Payload Metadata
Format: JSON-RPC notification (no response expected)
Latency: Minimal; triggers a tool list refresh
Real-World Implementation Use Case
An MCP server adds new database connection tools after a user completes OAuth; it sends `tools/list_changed` so the client updates its tool palette.
Cite This Page
MLA Style:
MCPserver.in Engineering. "MCP Tool List Changed." MCPserver.in Knowledge Hub, 20 July 2026, mcpserver.in/glossary/mcp-tool-list-changed.
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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