What Is agent-synapse in Claude Plugins? Multi-Session Communication Explained

agent-synapse is a Claude Code plugin that enables multiple Claude Code sessions to communicate across different projects via slash commands for messaging, inbox management, and presence detection.

The agent-synapse plugin bridges isolated Claude Code instances within the anthropics/claude-plugins-community ecosystem, allowing developers to coordinate complex workflows like distributed code reviews or multi-service orchestration. By creating a lightweight communication "synapse" between sessions, the plugin transforms individual Claude Code agents into a coordinated network using the Multi-Client Protocol (MCP) infrastructure.

Core Functionality of agent-synapse

The plugin operates as an MCP server that maintains state across disconnected Claude Code instances. Each session registers with a unique identity and can participate in targeted or broadcast communication patterns without leaving the terminal interface.

Named Session Registration

Before communicating, each Claude Code instance must declare its identity using the create-session command. This establishes a routable endpoint within the synapse network.

/agent-synapse create-session --name=frontend-dev

Sessions persist their identity until explicitly terminated, allowing long-running agents to maintain consistent addressing for incoming messages across project boundaries.

Cross-Session Messaging

The primary utility of agent-synapse lies in its direct message passing capabilities between named sessions. Unlike file-based coordination or external chat systems, this enables synchronous context exchange within the Claude Code interface.

To send a targeted message to a specific session:

/agent-synapse send --to=backend-ops --msg="Deploy v2.3 to staging"

Recipients retrieve messages by checking their inbox:

/agent-synapse inbox

This returns a timestamped log of communications:

[frontend-dev] > 2024-09-09 14:32 – "Review PR #42"
[frontend-dev] > 2024-09-09 14:45 – "Run integration tests"

Presence and Broadcast Capabilities

The plugin maintains a registry of active sessions. Developers can query online status before attempting communication or broadcast urgent notifications to all connected agents.

List currently active sessions:

/agent-synapse list-online

Example output:

Online sessions:
 • frontend-dev
 • backend-ops
 • data-pipeline

Send system-wide notifications using broadcast:

/agent-synapse broadcast --msg="All agents, sync to schema v5"

Technical Architecture and Source Files

The agent-synapse plugin is distributed through the anthropics/claude-plugins-community repository while maintaining its implementation in a separate upstream codebase. The integration relies on specific manifest files that register slash commands with Claude Code's MCP infrastructure.

Marketplace Registration

The plugin entry resides in /.claude-plugin/marketplace.json within the community repository. This file declares the plugin's metadata, description, and source URL to Claude Code's marketplace system.

"Let multiple Claude Code sessions talk to each other across projects. Each session gets a name, sends messages, checks its inbox, and sees who's online."

According to the source, this entry points to the upstream implementation at https://github.com/DisposableByDefault/agent-synapse.git.

MCP Manifest Configuration

Within the plugin's own repository, the /.claude-plugin/plugin.json file serves as the MCP manifest. This configuration registers the /agent-synapse slash commands and defines the server-side messaging logic that handles routing between sessions.

The architecture separates marketplace discovery (handled by the community repo) from command execution (handled by the DisposableByDefault upstream), allowing independent versioning of the communication protocol while maintaining discovery through the centralized anthropics/claude-plugins-community index.

Summary

• agent-synapse enables real-time messaging between distinct Claude Code sessions across different projects via named session identities
• Four core operations: session creation (create-session), direct messaging (send), inbox retrieval (inbox), and presence management (list-online/broadcast)
• Slash command interface: All interactions use the /agent-synapse prefix within Claude Code chat, processed through the MCP protocol
• Dual-repository structure: Discovery occurs through /.claude-plugin/marketplace.json in anthropics/claude-plugins-community, while implementation lives in DisposableByDefault/agent-synapse
• Use cases: Distributed code reviews, multi-service deployment orchestration, and cross-project brainstorming sessions

Frequently Asked Questions

What is agent-synapse used for in Claude Code?

agent-synapse connects isolated Claude Code instances into a coordinated network, enabling development teams to distribute tasks across multiple projects or conduct distributed code reviews. It eliminates context switching between chat applications by keeping all agent-to-agent communication within the Claude Code terminal interface.

How do I install the agent-synapse plugin?

Install via the Claude Code plugin marketplace by selecting agent-synapse from the community listings. The marketplace entry in /.claude-plugin/marketplace.json references the upstream repository at DisposableByDefault/agent-synapse, which contains the required plugin.json MCP manifest for registering the slash commands.

Can agent-synapse communicate across different machines?

Yes. The plugin functions across network boundaries as long as each Claude Code session maintains connectivity to the MCP infrastructure. Sessions identify each other by their registered names (established via create-session) rather than local process IDs, enabling cross-machine coordination for distributed development teams.

What is the difference between send and broadcast commands?

The send command targets a specific named session using the --to parameter for private, directed communication, while broadcast distributes the message to all currently online sessions without specifying individual recipients. Use send for targeted tasks requiring specific agent attention, and broadcast for system-wide notifications like schema updates or deployment signals.

{
  "mcpServers": {
    "instagit": {
      "command": "npx",
      "args": ["-y", "instagit@latest"]
    }
  }
}