hermes-a2a Plugin Setup
Source repo: hermes-a2a (iamagenius00 on GitHub)
Hermes plugin for peer-to-peer agent communication via Google's A2A protocol. Zero external dependencies, pure Python stdlib.
Prerequisites
- Hermes Agent v2026.4.23+ (plugin API with register_command)
- CLI mode only (gateway does NOT load plugins)
Install Steps
- Clone repo and run install.sh — copies 7 files to plugins directory
- CRITICAL: Run
hermes plugins enable a2a— plugins are opt-in - Set A2A_ENABLED=true and A2A_PORT=8081 in environment
- Restart CLI session (plugin loads at session start)
Pitfall: Plugin Must Be Explicitly Enabled
The plugin system requires explicit enablement. After install, run:
hermes plugins enable a2a
Without this, the plugin is discovered but NOT loaded. User plugins are opt-in — only bundled backends auto-load.
Pitfall: Gateway Does NOT Load Plugins
Only CLI mode supports A2A. Gateway (Telegram/Discord/Feishu) won't start the A2A server. Plugin hooks only fire in CLI conversation loop.
Tools Exposed
| Tool | Description |
|---|---|
| a2a_discover | Check remote agent's Agent Card |
| a2a_call | Send message to remote agent |
| a2a_list | List configured remote agents |
Configuring Remote Agents
Add entries under a2a.agents in config yaml:
a2a:
agents:
- name: "friend"
url: "https://friend-a2a-endpoint.example.com"
description: "My friend's agent"
auth_token: "their-bearer-token"
Security
- Bearer token auth (localhost-only without token)
- 20 req/min rate limit per IP
- 9 prompt injection patterns filtered
- Outbound secrets redacted
- Audit log at a2a_audit.jsonl
Architecture
Remote Agent sends A2A JSON-RPC to localhost:8081 → task_queue.enqueue() → webhook trigger fires agent turn → pre_llm_call hook injects message into current session → agent replies with full context → post_llm_call captures response → response returned synchronously (120s timeout) → exchange persisted to a2a_conversations/
Files
| File | Purpose |
|---|---|
| init.py | Entry point, registers hooks/tools/server |
| server.py | A2A HTTP server + webhook + task queue |
| tools.py | a2a_discover, a2a_call, a2a_list |
| security.py | Injection filtering, redaction, rate limit |
| persistence.py | Saves conversations to disk |
| schemas.py | Tool schemas |
| plugin.yaml | Plugin manifest |
Routing Keywords (in skill-router.md)
A2A agent dialogue, inter-agent communication, send a message to another agent → A2A plugin