Saturn

DNS-SD for AI. Discover and call any model on your network with one query.

Saturn is a protocol — mDNS/DNS-SD service type _saturn._tcp.local. — that lets any OpenAI-compatible AI endpoint announce itself on a LAN. Clients discover and call it with stock tools.

# 1. Discover Saturn endpoints on your LAN (macOS/Linux, no install)
$ dns-sd -B _saturn._tcp .local
Browsing for _saturn._tcp.local
  Add  3 llama-3-8b._saturn._tcp.local.
  Add  3 whisper-v3._saturn._tcp.local.

# 2. Resolve and call one — same shape as OpenAI
$ curl http://llama-3-8b.local:8080/v1/chat/completions \
    -H 'content-type: application/json' \
    -d '{"model":"default","messages":[{"role":"user","content":"hi"}]}'
{"id":"...","choices":[{"message":{"content":"Hello!"}}]}

AI agents and LLMs: read AGENTS.md. ML systems researchers: read docs/how-to/for-researchers.md.

This repository is the artifact of a master's thesis at UC Santa Cruz (Joey Perrello, advised by Adam Smith). Thesis: Saturn: Zero-Configuration AI Service Discovery (eScholarship, 2026).

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Why Saturn

• Zero-config. No accounts, no per-app keys, no manual endpoint URLs. The same mechanism your laptop already uses to find printers.
• Transport-agnostic. Anything that can browse mDNS and speak HTTP is a conformant client — dns-sd, avahi-browse, Go, Python, Rust, TS, Lua.
• OpenAI-compatible by default. Discovered endpoints expose /v1/health, /v1/models, /v1/chat/completions. Drop the URL into any tool that takes a base_url.

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Same idea, other languages

Go

$ cd saturnd && go build -o saturnd ./cmd/saturnd
$ ./saturnd                                # browse + serve on :7827
$ curl http://localhost:7827/v1/agents     # discovered Saturn instances

Python

$ pip install saturn-ai
$ saturn discover                          # print every advertised service
$ curl $(saturn endpoint)/v1/models        # call the highest-priority one

TypeScript

import { createSaturn } from "ai-sdk-provider-saturn";
const saturn = createSaturn();
const services = await saturn.discover({ timeout: 2000 });
console.log(services[0].endpoint);

Full per-language details: docs/integrations/.

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Implementations

Seven reference clients across five languages and four mDNS libraries, sharing no Saturn-specific code. Interoperability comes from the wire format alone (Saturn.md:976).

Implementation	Language	mDNS library	What it does
saturnd/	Go	grandcat/zeroconf	Standalone discovery daemon; A2A/MCP surface
saturn/	Python	python-zeroconf	Reference package: discovery, server, beacon, CLI, Web UI
saturn-router/	Rust	mdns-sd	Router-edge build (~2 MB, runs on a $20 OpenWRT MIPS box)
ai-sdk-provider-saturn/	TypeScript	multicast-dns	Vercel AI SDK provider with circuit breaking + failover
vlc_extension/	Lua + Python	dns-sd CLI	Bridges Saturn into a non-AI-native host application
saturn-mcp/	TypeScript	multicast-dns	Discovery surfaced as MCP tools
Open WebUI plugin	Python	python-zeroconf	Single-file backend swap for Open WebUI

A post-thesis OpenCode fork (TypeScript, multicast-dns) demonstrates agentic workflow with tool calls and streaming; it lives outside the monorepo and is not part of the canonical seven.

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TXT record (the wire artifact)

Saturn carries everything a client needs in one DNS-SD TXT record:

version=1                                 # protocol version — required
api_type=openai                           # api shape — required
deployment=cloud                          # local | cloud | network — required
priority=10                               # lower preferred — required
api_base=https://openrouter.ai/api/v1     # cloud only
ephemeral_key=eyJhbGc...                  # short-lived JWT, cloud only
rotation_interval=300                     # seconds; default 300
features=chat,tools,vision                # capability hints

RFC 6763 §6.1 caps each TXT string at 255 bytes — JWTs fit, X.509 certs don't. That constraint shapes the credential design.

Full schema, RFC-style stability levels, and per-key prose: docs/reference/protocol/txt-keys.md.

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Beacons and ephemeral keys

A Saturn beacon dispenses credentials for a cloud upstream and never proxies inference traffic:

1. Mint a scoped sub-key against the upstream with a short expiration.
2. Embed it in the ephemeral_key TXT field.
3. Rotate before expiry; clients re-read TXT.
4. Clients call the upstream directly — the beacon never sees prompt or completion bytes.

The reference Python beacon defaults to a 10-minute key with a 5-minute rotation interval (Saturn.md:614–615). These are reference-implementation defaults, not protocol invariants. The design bounds the dominant secret-leakage failure mode — Meli et al. found 81% of GitHub-leaked secrets are never revoked; a short-lived sub-key is dead before any scanner reaches it.

Security posture. Beacon mode is for trusted local networks — the kind you'd plug a printer into. The sub-key's per-key spending cap is the actual security boundary; set beacon.max_budget_usd low if your threat model includes any device on the LAN. If that doesn't fit, use proxy mode — Saturn keeps the parent key server-side and proxies through its own authenticated /v1/* endpoints, gated by SATURN_RUNNER_TOKEN (CONFIG_FIELDS §A.2).

Full threat model, TLS posture, and X-Forwarded-For / SATURN_TRUSTED_PROXIES setup: docs/reference/protocol/security.md.

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Roles

Saturn names three roles and concentrates configuration in exactly one of them.

• Administrator — deploys services, sets priorities, manages credentials. The only role that touches configuration.
• Application developer — calls discover(); receives services with URLs and credentials populated. No auth logic, no billing integration.
• End user — connects to the network. Nothing else.

The cognitive walkthrough in the thesis shows the application-developer step count drops 19 → 4 (−79%) and the end-user count drops 7 → 0 (−100%). Asymptotic form: 12 + 19N + 7M (traditional) → 14 + 4N + 0M (Saturn) over N developers and M end users. Methodology and threats to validity: docs/how-to/for-researchers.md.

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What Saturn is not

• Not a Python package. The Python reference implementation is one of seven; the protocol is the contract.
• Not field-evaluated. The step-reduction and threat-model arguments are derived from a single-author cognitive walkthrough and a structured threat analysis. There is no user study and no production deployment yet.
• Not safe on AP-isolated networks. Enterprise WiFi (eduroam, many guest SSIDs) blocks client-to-client multicast. A hybrid mDNS+HTTPS-fallback path is designed but not shipped.
• Not authenticated per-device. Any device on the LAN can observe service advertisements. Saturn trusts the network operator the way a printer protocol does.

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Conformance

A Saturn implementation in any language is five steps:

1. Browse _saturn._tcp.local. with any DNS-SD library.
2. Resolve SRV + TXT for each instance.
3. Validate version=1 and parse the TXT keys.
4. Sort by priority; pick the lowest healthy (probe GET /v1/health).
5. Call the /v1/* HTTP API at api_base (cloud) or the SRV host:port (local / network).

That is the entire protocol surface. The full 30-minute walk-through, including a working publisher and client in three languages, lives at docs/tutorial/. The proposed v2 schema redesign is at docs/spec/v0.2/wire-format.md.

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Platform notes

• macOS. dns-sd is part of the system; nothing to install. Beacon caveat: if you run a Saturn beacon on a laptop, keep it awake (caffeinate -i saturn run <name>) — the Bonjour Sleep Proxy can serve a stale TXT after the host sleeps and the published ephemeral_key expires. See docs/concepts/mdns-background.md#addendum-bonjour-sleep-proxy-and-beacon-hosts.
• Linux. sudo apt install avahi-utils. Saturn requires Avahi ≥ 0.9-rc3; older builds are exposed to CVE-2025-68276 / 68468 / 68471. Ubuntu 24.04 LTS is patched.
• Windows. Install Bonjour Print Services. If saturn is not on PATH, use python -m saturn.

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Docs · Contributing · License

• Full documentation: docs/ (four tabs: Home / Tutorial / Integrations / Spec).
• Contributions merged after 2026-03-20 will not be reflected in the published thesis document.
• License: see LICENSE.