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Canton DEX

Adding a new trading pair

Listing a pair (say ETH/USDT) is one operator-signed contract, DexPair. That contract is a venue record — trading mode, fee schedule, active flag — and nothing more. It does not by itself make the market tradable: order-book mode needs the registry’s Token Standard V2 factories behind each asset, and pool mode needs a pool that a first liquidity provider has funded. This recipe creates the listing, then does whichever of those the pair requires.

It assumes the operator backend is already wired to a participant, and that the base and quote assets already have registries producing V2 holdings, allocation factories, and settlement factories. If either asset lacks a V2-compatible registry, do that first — see add-lp-or-instrument.md — because pair creation will succeed but trades will not flow.

What a listing is, and what it isn’t

Section titled “What a listing is, and what it isn’t”

DexPair is signed by the operator and observed by the pair’s registry admin (plus any publicReaders):

signatory operator
observer admin :: optional [] identity publicReaders

So the operator owns the listing, the admin can see it, and traders see it only if you add them as public readers. The listing carries the trading mode and fee model; tradability comes from elsewhere:

flowchart TB
  L["DexPair — operator-signed listing tradingMode · feeModel · active"]
  L -->|"TM_OrderBook / TM_Both"| OB["Order book: tradable once the registry publishes V2 allocation + settlement factories for both assets"]
  L -->|"TM_Pool / TM_Both"| P["Pool: tradable once createPool + the first-LP DvP move it PS_Unfunded → PS_Active"]

Inputs you need

Section titled “Inputs you need”
Input Where it comes from
baseInstrumentId : Text the id component of the base asset’s V2 InstrumentId; full identity is { admin, id }
quoteInstrumentId : Text same, for the quote asset
admin : Party the registry admin for the base + quote instruments
tradingMode : "TM_OrderBook" | "TM_Pool" | "TM_Both" which surfaces are enabled
feeModel : { makerFeeBps, takerFeeBps, poolFeeBps } fee schedule, in basis points
publicReaders : [Party] (Optional) parties that should observe the listing

Step 1 — List the pair (DexPair)

Section titled “Step 1 — List the pair (DexPair)”

Operator-signed, submitted by the operator backend:

Terminal window
curl -X POST http://localhost:8080/v1/admin/pairs \
  -H "Authorization: Bearer $OPERATOR_ADMIN_TOKEN" \
  -H 'Content-Type: application/json' \
  -d '{
    "baseInstrumentId": "ETH",
    "quoteInstrumentId": "USDT",
    "admin": "<admin-party>",
    "tradingMode": "TM_Both",
    "feeModel": {"makerFeeBps": 10, "takerFeeBps": 30, "poolFeeBps": 30},
    "active": true
  }'

The route calls AdminService.createPair in services/operator-backend/src/admin/index.ts, which submits one create for CantonDex.Dex.DexPair:DexPair as the operator:

this.ledger.submit<ContractId<"DexPair">>({
  actAs: [this.operatorParty],
  commandId: `pair-create:${input.baseInstrumentId}:${input.quoteInstrumentId}`,
  command: {
    kind: "create",
    templateId: "CantonDex.Dex.DexPair:DexPair",
    argument: { operator: this.operatorParty, admin: input.admin, /* … */
      active: input.active ?? true, publicReaders: null, /* … */ },
  },
});

Response: { pairCid: ContractId<DexPair> }. Note it. If tradingMode is TM_OrderBook, the listing is complete — traders can now post V2-allocation-backed orders, provided the registries publish the required factories.

Step 2 — For pool mode, create the pool

Section titled “Step 2 — For pool mode, create the pool”

TM_Pool and TM_Both need a pool. One admin call provisions everything the pool needs:

Terminal window
curl -X POST http://localhost:8080/v1/admin/pools \
  -H "Authorization: Bearer $OPERATOR_ADMIN_TOKEN" \
  -H 'Content-Type: application/json' \
  -d '{
    "baseInstrumentId": "ETH",
    "quoteInstrumentId": "USDT",
    "lpInstrumentId": "ETH-USDT-LP",
    "lpRegistrar": "<lp-registrar-party>",
    "admin": "<admin-party>",
    "feeBps": 30
  }'

AdminService.createPool creates, in one flow: the immutable Pool config, its PoolState in PS_Unfunded, the per-venue PoolRules, the co-signed PoolLiquidityRules (operator + lpRegistrar), and the matching CantonDex.Lp.Policy:LPTokenPolicy. There is no separate LP-policy step — creating the pool creates the policy. Response: { poolCid: ContractId<Pool> }.

Because the LP policy is signatory lpRegistrar and PoolLiquidityRules is signed by both parties, the backend must be authorized to submit as both the operator and the lpRegistrar. The pool starts with no reserves and is not tradable; the first LP funds it in Step 3.

The pool’s executable swap fee is the pool’s own feeBps set here — the pair’s feeModel.poolFeeBps is a listing-level record, not the number the curve charges.

Step 3 — Seed the first liquidity (pool mode)

Section titled “Step 3 — Seed the first liquidity (pool mode)”

The first LP moves the pool from PS_Unfunded to PS_Active through the same add-liquidity DvP used for every later deposit:

  1. Hold V2 base and quote holdings of the amounts to deposit.
  2. POST /v1/pools/add-liquidity/request — returns the request plus the allocation specs and factory contract ids the wallet needs.
  3. The wallet authors the three requested allocations with AllocationFactory_Allocate: base deposit, quote deposit, and the LP receipt.
  4. POST /v1/pools/add-liquidity/settle — operator and lpRegistrar co-settle via PoolLiquidityRules_SettleAddLiquidity, which seeds the first pool slices, transitions the pool to PS_Active, and mints sqrt(baseAmount * quoteAmount) LP tokens atomically.

Step 4 — Surface and verify

Section titled “Step 4 — Surface and verify”

The dApp’s /v1/pairs returns the new listing and the Pools page shows the pool once it is seeded. The current Trade page is pool-driven: it reads active pools and does not filter them through DexPair.active or tradingMode. Treat those fields as discovery metadata unless your application adds an off-ledger filter or an on-ledger terminal-choice gate.

Terminal window
curl -s http://localhost:8080/v1/pairs | jq '.[] | select(.baseInstrumentId=="ETH")'
curl -s http://localhost:8080/v1/pools | jq '.[] | select(.baseInstrumentId=="ETH")'

After the first seed, liquidity and swap events show up on /v1/swaps:

Terminal window
curl -s 'http://localhost:8080/v1/swaps?pair=ETH/USDT&limit=10'

Common pitfalls

Section titled “Common pitfalls”
Symptom Cause
/v1/admin/pools fails with an authorization error The backend can only act as the operator. Pool creation submits the co-signed PoolLiquidityRules and the lpRegistrar-signed LPTokenPolicy, so the backend must be authorized to act as both the operator and the lpRegistrar.
DexPair created but absent from /v1/pairs The backend isn’t observing the new contract; check the backend’s operator party matches the pair’s operator signatory.
Pool created but /v1/pools is empty Pool is observed only by operator + lpRegistrar. The backend reads as operator; a different signing party won’t be seen.
/v1/pools/add-liquidity/request or /settle fails with an allocation mismatch The wallet-authored allocation triple doesn’t match the request’s expected specs; recreate the request and re-author from that payload.
/settle fails with a quote/supply guard The pool moved or the request expired before settle; recreate the request and re-author fresh allocations.
Trades fail even though DexPair exists The listing is only a venue record. The registries still need to publish V2 holdings, allocation factories, settlement factories, and any required choice context for the instruments.

Reference: post-listing lifecycle choices

Section titled “Reference: post-listing lifecycle choices”

After listing, the operator adjusts the pair through DexPair’s own choices — all controller operator — each fronted by an admin route:

Choice Route
DexPair_UpdateFeeModel POST /v1/admin/pairs/{pairCid}/fee-model
DexPair_SetActive POST /v1/admin/pairs/{pairCid}/active
DexPair_UpdateTradingMode POST /v1/admin/pairs/{pairCid}/trading-mode
DexPair_UpdatePublicReaders (no admin route; submit via the backend)

Listing many pairs at once is a script, not a curl loop: build every create command in one batch keyed off your asset list, and never list a pair whose base or quote lacks a V2 registry — the listing will exist, but no wallet can create or settle the holdings and allocations a trade requires.

What proves this

Section titled “What proves this”

Where to read next: Add an LP or Instrument · Builder Guide · All docs