Auction Only Order Types For Illiquid Names

When to Use

Use this execution algorithm when attempting to buy or sell a large block of an illiquid equity (e.g., small-cap or micro-cap stocks). Trading illiquid names during the continuous market session often leads to catastrophic market impact (slippage) as the order "walks the order book."

This skill leverages the centralized liquidity event of the exchange's Closing Auction by routing the order as a Limit-on-Close (LOC) order, significantly reducing information leakage and price impact.

When NOT to Use

Do NOT use it to provide contra-side liquidity against a published closing imbalance — that is close-auction-participation-strategy, which consumes the NOII/NYSE imbalance feed this skill deliberately does not read. It is also not an order gateway: it produces routing and pricing parameters, it does not submit, amend or cancel orders.

Prerequisites

• Python 3.10+ (the module uses zoneinfo; on a bare Windows or slim container

install the tzdata package so America/New_York resolves).

• Average Daily Volume (ADV) metrics for the target instrument.
• The scheduled session close for the trading date, not just the current

time. Every deadline below is defined relative to it: NYSE's MOC/LOC entry deadline is the Closing Auction Imbalance Freeze Time, ten minutes before the scheduled end of Core Trading Hours (NYSE Rule 7.35(a)(8)), so on a 1:00 p.m. early-close day it is 12:50 p.m., not 3:50 p.m. Pass market_close_et=EARLY_CLOSE_SESSION_CLOSE_ET on half days.

• Which venue's rules apply. On a regular 4:00 p.m. ET close: NYSE accepts

unconditional MOC/LOC entry until 3:50 p.m.; Nasdaq rejects MOC at or after 3:55 p.m. and LOC at or after 3:58 p.m. Both freeze free cancel/modify at 3:50 p.m. CLOSING_AUCTION_CUTOFF_ET (3:50 p.m.) is the conservative, exchange-portable default; entry_cutoff_for(venue, order_type, market_close_et) gives the venue-specific deadline.

• A reference price (e.g. current mid-price), a slippage tolerance, and the

instrument's minimum price variation to derive the LOC limit price. An LOC order is a limit order (NYSE Rule 7.31(c)(2)(A), Nasdaq Equity 4 Rule 4702(b)(12)(A)) and requires a limit price at submission.

Workflow

1. Liquidity Assessment: Evaluate the order size against the instrument's Average Daily Volume (ADV).
2. Strategy Routing via IlliquidAuctionExecutionEngine.generate_routing_plan():

• If the order is massive relative to ADV (>=5%), attempting to execute it in the continuous market is dangerous. The engine routes 100% of the order to the Closing Auction via LOC.
• If the order is moderate (1%-5% of ADV), the engine uses a hybrid approach: slicing a portion into continuous trading (e.g., VWAP) and reserving the remainder for the Closing Auction.
• If the order is small (). Do not compare wall clocks yourself — pass a timezone-aware datetime in any zone and the module converts it to America/NewYork first. For a venue-specific deadline, pass cutoff=entrycutofffor(venue, ordertype, marketcloseet)`.

1. Late-window handling: Clearing the cutoff is necessary but not sufficient. Between the NYSE freeze time and the close, NYSE accepts only MOC/LOC orders contra to a published Significant Closing Imbalance and rejects all others; a Nasdaq LOC entered in its final three minutes is accepted only against a First or Second Reference Price and, if more aggressive than it, is rejected or re-priced to it. Unless you are consuming the imbalance feed (see close-auction-participation-strategy), treat the conservative cutoff as final.
2. Commitment: Auction quantity resting at the freeze time cannot be freely pulled — cancel_modify_freeze_for(market_close_et). Size it as capital committed to trading at an unknown closing price.

Common Pitfalls

• Using MOC instead of LOC for Micro-Caps: A massive MOC order on a micro-cap stock guarantees execution, but the resulting auction imbalance can cause the closing price to gap 10% away from the fair value. Always use LOC for illiquid names.
• Assuming MOC and LOC share one deadline: on Nasdaq they do not. MOC entry is rejected at or after 3:55 p.m. ET; LOC survives until 3:58 p.m. Hard-coding a single "on-close cutoff" either rejects legal LOC entries or sends MOC orders the venue will reject.
• Hard-coding 3:50 p.m. as the cutoff: NYSE deadlines are tied to the scheduled end of Core Trading Hours and move on early-close days. On a 1:00 p.m. half day the MOC/LOC deadline is 12:50 p.m.; an algorithm holding a fixed 15:50 constant will believe it has three more hours and miss the auction entirely. Always pass the session's scheduled close.
• Comparing a non-Eastern wall clock to an ET cutoff: 12:55 US/Pacific is 15:55 ET, five minutes past the NYSE deadline, but its raw time-of-day reads as safely early. is_past_closing_auction_cutoff and validate_submission_window convert to America/New_York first and reject naive datetimes outright.
• Submitting an LOC without a limit price: An LOC is a limit order and will be rejected by the exchange without one. If reference_price was not supplied to generate_routing_plan, suggested_limit_price will be None and the caller must assign a limit price before submission.
• Sending a sub-penny limit price: 20.01 * 1.005 = 20.11005. Submitting 20.1101 on an NMS stock priced at or above $1.00 is not a permissible minimum increment under SEC Rule 612 and the venue rejects it. The engine rounds to tick_size, and rounds away from the aggressive side so the rounding can never breach the caller's slippage tolerance.
• Treating the auction leg as cancellable: after the freeze time (3:50 p.m. on a regular close) NYSE will not cancel or reduce an MOC/LOC order even to correct a legitimate error, and Nasdaq permits only legitimate-error corrections. Quantity sent to the auction is committed.

Verification

Run python -m unittest discover -s skills/auction-only-order-types-for-illiquid-names/scripts to confirm that the engine allocates orders to LOC based on their size relative to the ADV, derives a tick-compliant suggested limit price that never breaches the slippage tolerance, validates its inputs, converts submission timestamps to US/Eastern before comparing them, and derives closing-auction cutoffs from the scheduled session close for both regular and early-close days.

Spot checks:

• A buy at reference_price=20.01 with the default 50 bps tolerance yields 20.11, not 20.1101.
• is_past_closing_auction_cutoff(datetime(2024, 3, 1, 12, 55, tzinfo=US/Pacific)) is True — that instant is 15:55 ET.
• entry_cutoff_for(AuctionVenue.NASDAQ, OrderType.MARKET_ON_CLOSE) is 15:55, while the LOC cutoff is 15:58.
• entry_cutoff_for(AuctionVenue.NYSE, OrderType.LIMIT_ON_CLOSE, EARLY_CLOSE_SESSION_CLOSE_ET) is 12:50.

Related Skills

• close-auction-participation-strategy
• minimum-fill-size-and-lot-rounding-logic
• global-exchange-holiday-calendar-handling
• clock-synchronization-ptp-for-trading-hosts
• exchange-tick-size-regime-tracking

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: HimanshuJ16
• Source: HimanshuJ16/Algo-Trading-Skills
• License: Apache-2.0
• Homepage: https://skills.himanshujangir.com

Install and usage instructions live in the source repository linked above.