arcus-agent-gateway

An MCP (Model Context Protocol) server that gives AI agents read-only, keyless access to market data for the 194 tokenized US equities on Robinhood Chain (Arcus) — quotes, corporate actions, trading capabilities, multipliers and a 13-sector map. No API keys, no auth, no writes: every tool is a GET against the public api.robinhood.com/rhj REST surface, cached and rate-limited so an enthusiastic agent can't hammer the upstream.

Quickstart

Run over stdio (the default, for local agents):

uvx arcus-agent-gateway

Claude Desktop / Cursor config (claude_desktop_config.json or .cursor/mcp.json):

{
  "mcpServers": {
    "arcus": {
      "command": "uvx",
      "args": ["arcus-agent-gateway"]
    }
  }
}

Hosted form — streamable HTTP on port 8902:

uvx arcus-agent-gateway --http               # 127.0.0.1:8902
curl http://127.0.0.1:8902/health            # -> {"ok": true, "service": "arcus-agent-gateway"}

Tools

All 9 tools are read-only (annotated readOnlyHint: true). Names and parameters are exactly as registered by arcus_mcp/server.py.

Multiplier logic (read this before using prices)

Robinhood Chain tokens carry a multiplier — the corporate-action adjustment factor for the token contract (1.0 = untouched). Splits change it; for example NVDA's 2026-11 split queues pendingMultiplier: "4.0".

• The REST API returns RAW prices. bid/ask from /prices/{symbol} are in token-contract units and are not multiplier-adjusted.
• Adjusted values are computed by this server, never taken from upstream: price_adjusted = round(price_raw × currentMultiplier, 6).
• Raw and adjusted always travel together. Every quote carries bid_raw/ask_raw/spread_raw and bid_adjusted/ask_adjusted/ mid_adjusted next to the multiplier block — never one without the other.
• On-chain quantities (token balances, mint/burn volumes) are natively in adjusted (multiplied) units; REST prices are not. If you compare the two, go through the *_adjusted fields.

Worked example (live fixture, 2026-09-03):

AAPL   currentMultiplier = 1.000566080061092436
       bid_raw   = 327.77   →  bid_adjusted = round(327.77 × 1.000566…, 6) = 327.955544
       ask_raw   = 327.78   →  ask_adjusted = 327.965550
       mid                      mid_adjusted = 327.960547

Pending split warning. When pendingMultiplier is queued (non-empty) and differs from the current one, token_detail() adds a warning like pending split: 1→4.0 on 2026-11-06T00:00:00Z, and quote()'s multiplier block exposes pending + effective_time. After the split lands, raw prices jump by the ratio while *_adjusted fields stay comparable — another reason to always read adjusted values next to the multiplier.

API limits & caching

• Upstream allows 60 req/s without a key; this client self-limits to ≤ 50 req/s (a 20 ms politeness interval between requests, thread-safe).
• Transient failures (429/502/503/504, network errors) are retried up to 3 times with 2s × (attempt+1) backoff.
• Response caches (per process): /assets 5 min, /prices/{symbol} 15 s, /corporate-actions 1 h. market_status() and sector_view() are computed from caches and assets only — they never fan out 194 price requests.

Raw prices disclaimer

Prices are served exactly as they arrive from Robinhood (RAW) — they are not multiplier-adjusted, and the *_adjusted fields are our computation, not upstream data. All data is for information only, not for trading decisions, and should be verified against the official source before you act on it. No warranty of completeness, accuracy or timeliness.

Development

python3 -m venv .venv && .venv/bin/pip install -e '.[dev]'
.venv/bin/pytest -q                      # 75 tests, all offline (fixtures + mocks)
.venv/bin/python scripts/smoke_api_offline.py     # REST client smoke, zero HTTP
.venv/bin/python scripts/smoke_server_offline.py  # 9-tool server smoke, zero HTTP

Layout: arcus_mcp/api.py (stdlib REST client), arcus_mcp/server.py (9 MCP tools + FastMCP wiring), arcus_mcp/sectors.py (validated 13-sector map), arcus_mcp/paths.py (state dir; override with ARCUS_GATEWAY_DATA). Live-captured schema fixtures live in tests/fixtures/ with notes in arcus_mcp/API_NOTES.md. Usage scenarios: examples/use-cases.md.