bacnh85 A2A — Agent-to-Agent Protocol v1.0
Pi as a first-class A2A peer. A2A is the open Linux Foundation standard for inter-agent communication (JSON-RPC 2.0 over HTTP). This extension makes Pi bidirectional: it can call other agents and be called by them.
When to use
- Delegating to a specialist — a peer advertising
web_search/research/codingskills can be discovered and called mid-conversation. - Cross-machine collaboration — hand a task to a Hermes on a server, each with its own memory/tools/credentials.
- Parallel fan-out — send one task to every capable peer at once.
- Being callable — expose Pi so other frameworks' agents can send it tasks.
For same-machine, in-process delegation (cheaper, shared context) prefer the
subagent tool. A2A is for crossing process/machine/framework boundaries.
Outbound — calling other agents (5 tools)
| Tool | Use |
|---|---|
a2a_discover(url) |
Fetch a peer's Agent Card to learn its capabilities |
a2a_call(agent, message, context_id?) |
Send a task, get the reply; reuse context_id for multi-turn |
a2a_list() |
Configured peers, persisted conversations, metrics |
a2a_history(context_id) |
Recall a persisted conversation |
a2a_orchestrate(capability, message, mode?) |
Fan-out to all peers advertising a capability (all/first/best) |
agent is a configured peer name (from a2a.peers in settings.json) OR a full
http(s):// URL.
Inbound — being callable (opt-in)
/a2a-server start serves an Agent Card + JSON-RPC endpoint. Each inbound task
spawns an isolated Pi agent session in the workspace and returns the reply as a
task artifact. Localhost-only by default; remote needs a token + explicit host.
Commands
/a2a-discover <url> · /a2a-agents · /a2a-send <agent> <msg> ·
/a2a-broadcast <msg> --agents a,b,c · /a2a-status · /a2a-config ·
/a2a-server start|stop|status · /a2a-help
Security (on by default)
- No token ⇒ localhost-only bind; remote requires token + explicit host.
- Outbound text is scrubbed of credentials; inbound text is injection-filtered and framed as untrusted peer input.
- Per-context anti-loop cap; append-only audit log at
<piDir>/a2a_audit.jsonl.
Configuration
Peers and server live under the a2a key in ~/.pi/agent/settings.json, or
A2A_* env vars. See the package README for the full schema.