> For the complete documentation index, see [llms.txt](https://docs.nexus.xyz/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.nexus.xyz/exchange/apis-and-rates/market-maker-guide.md).

# Market Maker Guide

Everything a market maker needs to integrate with the Nexus Exchange. The exchange is API-first — there is no MM-specific UI; you quote, cancel, and stream over the same REST + WebSocket surface every client uses, with a higher rate tier and a maker-only order type.

For the primitives, this guide points at the reference pages rather than restating them: [REST](/exchange/apis-and-rates/exchange-rest.md), [WebSocket](/exchange/apis-and-rates/exchange-websocket.md), [Rate Limits](/interfaces/rate-limits.md), [Rate & Connection Limits](/exchange/apis-and-rates/rate-limits.md), and the [Quickstart](/exchange/trading/quickstart.md).

## 1. Get MM-tier access

The **Market Maker** rate tier (**a budget of 2,000 weight per second**, of which a plain order submit costs 1) is admin-assigned, not self-serve — see [Rate Limits](/interfaces/rate-limits.md) for how requests are costed. Request the tier via your Nexus contact with your `key_id`. Until promoted, a key runs at the base tier. MM keys also get higher WebSocket ceilings (100 simultaneous connections vs. 5 at base, and 1,000 subscriptions vs. 50).

> Testnet-preview note: tier assignment and rate-limit state are currently in-memory at the gateway and reset on restart — after a gateway redeploy an MM key may briefly fall back to base until re-promoted. Note also that a key carries its own ceiling from the moment it was created (20/s by default) and a promotion does not rewrite it: check `GET /account/rate-limit` after being promoted, since the effective limit is whichever of the two binds first, and mint a fresh key if it still reports the base number.

## 2. Authenticate

Standard flow (details in the [section overview](/exchange/apis-and-rates.md)): wallet-signed session token (EIP-191) to create an **HMAC API key**, then sign every request with the key. The session token is for key management only — never for trading. Keep the HMAC secret safe; it's shown once.

## 3. The maker order surface

The order type that matters most for market making:

* **Post-only** — set `time_in_force: "PostOnly"` on a limit order. The engine **rejects** the order (rather than filling) if it would cross the book and take liquidity on entry, guaranteeing you rest as a maker. A crossing post-only order comes back as an `InvalidOrder` with code **`WouldTakeLiquidity`** — detect that and re-quote. This is the primary tool for never paying taker fees.
* Standard `GTC` / `IOC` / `FOK` are also available for the non-resting cases.
* **Batch + cancel-all.** Use batch order placement to refresh a quote ladder in one request, and market-scoped cancel-all to pull quotes on a market quickly. Amend is available for in-place price/size changes. (See [REST reference](/exchange/apis-and-rates/exchange-rest.md).)

## 4. Stream the market

Subscribe over [WebSocket](/exchange/apis-and-rates/exchange-websocket.md) rather than polling:

* **Order book** and **trades** for the market data you quote against.
* **Your fills / orders / positions** (private channels) to track quote state — mint a single-use ws-token via `POST /ws/token`, then connect.

Connection and subscription caps are per-tier (MM: 100 connections, 1,000 subscriptions) and form their own budget, separate from the REST one — see [Rate Limits](/interfaces/rate-limits.md). Subscriptions are capped per connection *and* across all of an account's connections at the same number, so spreading a quote ladder over more sockets does not raise the total. Design for reconnect: the client should re-subscribe and re-sync book state on reconnect, and a resubscribe storm is covered by the 2× inbound-frame burst allowance.

## 5. What to expect on latency & throughput

**We do not publish a latency figure for this venue yet.** Earlier revisions of this page carried an order-to-ack p95 and a WebSocket delivery p95 that were internal engineering targets, not measurements of the deployed testnet preview. Both have been removed rather than restated: a latency number a desk cannot reproduce is worse than no number at all.

What we can tell you today:

* **Rate ceiling, not a measured capacity.** The MM tier admits **2,000 weight per second** per key (see [Rate & Connection Limits](/exchange/apis-and-rates/rate-limits.md)). That is the configured admission ceiling — it is not a measured saturation point and it is not a throughput commitment. Pace against the `x-ratelimit-*` headers on every response and back off on `429` + `retry-after`, remembering two things about what those headers mean: `x-ratelimit-remaining` counts **unit-cost** requests, so it overstates how many heavy reads are left; and order writes draw on a **separate** budget from reads, so a healthy `remaining` on your last read says nothing about placement headroom.
* **Latency: measure it from your own client, and hold us to what you measure.** The numbers that matter to a quoting strategy — REST order-to-ack round trip, and matching-event-to-WebSocket-frame delivery — depend on your network path as much as on us, so your own measurement is the one worth acting on. Tell your Nexus contact what you get; a reproducible client-side number from a real desk is more useful to us than an internal one.
* **Latency goals tighten across release gates**, as noted in the [WebSocket reference](/exchange/apis-and-rates/exchange-websocket.md). When we publish a figure it will carry its conditions: environment, client location, network path, offered load, what the timer starts and stops on, and percentiles from a single run rather than averaged across runs.

## 6. Tooling

* **SDKs:** Rust (`nexus-exchange` on crates.io), Python (`nexus-exchange` on PyPI — the repository is `nexus-exchange-py`), and TypeScript (`@nexus-xyz/exchange-ts` on npm) all wrap this API, including request signing.
* **CLI:** `nexus-exchange-cli` (`nexus`) is a thin command layer over the Rust SDK.
* **CCXT:** the API exposes CCXT-compatible endpoints (tagged in the OpenAPI spec), so existing CCXT-based MM tooling connects with minimal changes.

## 7. Testnet status

This is a testnet preview: balances are testnet USDX (no real funds), state can reset on redeploy, and tier/rate-limit ceilings are configurable and may change as the tier system is finalized across release gates. Treat API keys as re-creatable.

***

*Doc note (ENG-2755): the per-tier ceilings now live in exactly one published place —* [*Rate Limits*](/interfaces/rate-limits.md) *— so this guide names only the MM figures it needs and links for the rest. The earlier Pro-tier inconsistency (ENG-4062: 200 req/s published vs. `DEFAULT_PRO_RPS` = 20 in code) is resolved; the published number is 20, matching the code.*


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