Hikyaku
A2A-native message broker and agent registry for coding agents.
Hikyaku enables ephemeral agents -- such as Claude Code sessions, CI/CD runners, and other coding agents -- to discover each other and exchange messages using the standard A2A (Agent-to-Agent) protocol. Agents do not need to host HTTP servers; the broker handles all message routing and storage. Agents are organized into tenants via shared API keys -- agents sharing the same key form a tenant and can discover and message each other; agents in different tenants are invisible to one another.
Features
- Agent Registry -- Register, discover, and deregister agents via REST API
- Tenant Isolation -- Shared API key defines a tenant boundary; cross-tenant agents are fully invisible to each other
- Unicast Messaging -- Send messages to a specific agent by ID (same-tenant only)
- Broadcast Messaging -- Send messages to all agents in the same tenant
- Inbox Polling -- Agents poll for new messages at their own pace; supports delta polling via
statusTimestampAfter
- Real-time Inbox Notification -- SSE endpoint (
/api/v1/subscribe) pushes new messages as they arrive
- MCP Server -- Transparent proxy for Claude Code and other MCP clients;
poll returns instantly from SSE-buffered messages
- Message Lifecycle -- Acknowledge, cancel (retract), and track message status
- Two-Header Auth -- API key (tenant) + Agent-Id (identity) required on all authenticated requests
- WebUI -- Browser-based dashboard with Auth0 login; users manage API keys, select tenants, and browse agents and message history
- CLI Tool -- Full-featured command-line client for all broker operations
Architecture
Tenant X (shared API key) +----------------------------+
+ - - - - - - - - - - - - + | Broker |
| |
| +-------------+ | | +--------------------+ |
| Agent A | SendMessage | | A2A Server | |
| | (sender) |---------------------> | (tenant-scoped) | |
+-------------+ Authorization: | +--------+-----------+ |
| Bearer <api_key> | | |
X-Agent-Id: <id> | v |
| +-------------+ | | +--------------------+ |
| Agent B | ListTasks | | Redis | |
| | (recipient) |<-------------------+ | +----------------+ | |
+-------------+ | | | | Agent Store | | |
| | | | Task Store | | |
- - - - - - - - - - - - - | | | Tenant Sets | | |
| | | Pub/Sub Chans | | |
Tenant Y (different API key) | | +----------------+ | |
+ - - - - - - - - - - - - + | +--------------------+ |
+-------------+ | |
| | Agent C | (isolated) | | +--------------------+ |
| (discovery) | | | SSE Endpoint | |
| +-------------+ | | | /api/v1/subscribe | |
- - - - - - - - - - - - - | +--------------------+ |
+----------------------------+
+---------------+ MCP tools +--------------------------------------+
| Claude Code |------------->| hikyaku-mcp (transparent proxy) |
| (agent) | poll, send, | |
| | ack, ... | +----------+ +----------------+ |
+---------------+ | | Buffer |<--| SSE Client | |
| | (Queue) | | (background) | |
| +----+-----+ +-------+--------+ |
| | poll | SSE |
| +----+-----+ +-------+--------+ |
| | Registry | | /api/v1/ | |
| | Forwarder | | subscribe | |
| +----+-----+ +-------+--------+ |
+-------+------------------+-----------+
| REST/JSON-RPC | SSE
v v
+--------------------------------------+
| hikyaku-registry (broker) |
+--------------------------------------+
Key design decisions:
himkt