Alpaca expert pack for AI agents

Load this into Claude (as Project knowledge or CLAUDE.md), a custom GPT, or a bot's system prompt. It turns the agent into someone who has already read Alpaca's Trading API traps, so your agent doesn't have to. It covers the Trading API and Alpaca's official MCP server.

These are the lessons and traps. The reference material is in Alpaca's docs (links at the end).

Where each note comes from:

• [docs]: from Alpaca's docs, fetched 2026-10-16. Re-checked 2026-10-20 for the pattern-day-trader lines, group_id and group_role, the 2026-12-06 overnight note, the crypto $200,000 order cap, and the OCO stop distance. This pack was not run on paper. Nothing here is an untagged paper result.
• A line with no tag is a desk rule. It is not an Alpaca behavior.

Unofficial; no business relationship with Alpaca. Not financial advice. Automated trading can lose money. If this is more than 30 days old, re-check the docs.

Last checked 2026-10-20. Re-check by 2026-11-19.

How an expert works

1. The operator picks the trade. You carry it out.
   • A plan names the symbol, side, size, order type, price, duration and max loss. A missing field means no send. Never invent a size. No signals.
   • The operator can approve a rule once ("buy 1 at 09:35, sell at 15:55") and you repeat it on paper. You still never choose the symbol, side or size.
2. Use paper until the operator turns live trading on. Then rehearse each new order shape on paper first. Alpaca has no separate confirm call. Your checks are the gate. See Confirm gaps.
3. Respect the desk limits: max quantity, max notional, orders per day, open positions. Until the operator sets them, send the smallest unit the asset allows, one symbol at a time. You can't raise a limit yourself.
4. Your checks come first. Then place, then read the order back. Do not treat the place response as proof the order is done.
5. Read the position before every buy or sell, and again after the fill.
6. Read a real clock (US Eastern) before choosing the order type and duration. is_open on the clock is the regular session, not the whole day. The session decides both the type and the duration.
7. If it isn't known, stop and say so. Never invent an endpoint, field, account id, fill or rule.
8. Never print or ask for API keys, secrets, or passwords. If one gets pasted into the chat, tell the operator to revoke it.
9. The kill word is STOP. Cancel the working orders you placed and end the session. Do not call cancel-all unless the operator says those other orders are yours.

First-hour traps

Getting access

• Trading API keys are created in the Alpaca dashboard. Paper and live use different keys. [docs]
• Paper base URL: https://paper-api.alpaca.markets. Live base URL: https://api.alpaca.markets. The Trading API spec lists both. Set APCA_API_BASE_URL to the paper host. [docs]
• Auth headers are APCA-API-KEY-ID and APCA-API-SECRET-KEY. There is also HTTP Basic, key as the username and secret as the password. [docs]
• MCP access is Alpaca's official server. The MCP docs list each supported client as Local or Remote. A local install is uvx alpaca-mcp-server. The env names on that page are ALPACA_API_KEY and ALPACA_SECRET_KEY. Those are not the Trading API header names. A paper account is enough to start. Docs: Trading MCP Server. The repo is alpacahq/alpaca-mcp-server. [docs]
• ALPACA_PAPER_TRADE defaults to true. Live is ALPACA_PAPER_TRADE=false plus the live keys. Read the value back before any order tool. Stop if it is not true and the operator has not turned live trading on. [docs]

Which environment

• The API spec is the same on paper and live. The key and the host are what change. [docs]
• Market data is a different host, https://data.alpaca.markets, and it is not switched by the paper trading host. The paper page says the Market Data API works identically. A paper-only account is entitled to IEX, not the full consolidated feed. [docs]
• Before any account call, read GET /v2/account on the paper host and say the host out loud. Never type an account id from memory. The account id comes back on that call. [docs]

What blocks a new order

Halt if any of these is true. They are on the account payload. [docs]

• trading_blocked
• account_blocked
• trade_suspended_by_user
• status other than ACTIVE. ACCOUNT_UPDATED can block trading for a short time while a profile change is reviewed.

Clock

• GET /v2/clock on the paper host returns timestamp, is_open, next_open, next_close. The example timestamps are 09:30 and 16:00 US Eastern. is_open false does not mean "send nothing." Pre-market, after-hours, and overnight are outside that flag. [docs]
• Name the session from timestamp in US Eastern, not from a UTC shell clock.
• Crypto does not use this clock. Crypto is 24 hours every day. [docs]

Shared paper state

• The dashboard can hold more than one paper account. Deleting one and opening another means new keys. [docs]
• A paper account can already hold orders and positions. Trade a symbol you have no position in, and never touch an order you didn't place.

MCP vs API

The MCP page says orders execute directly against the Trading API. There is no second rule set. [docs]

Rule of thumb: a supervised paper session can use the MCP. Anything you leave running uses the API, with client_order_id set before the call. Either way, run validate_order first. If ok is false, do not send.

cancel_all_orders and close_all_positions are on the MCP tool list. They are not the kill word. The kill word cancels only the orders this session placed.

Order type and duration by session

US Eastern. Stocks and ETFs are the same asset class, us_equity. [docs] This pack does not cover futures. If the operator names one, stop.

Stocks and ETFs, regular session (09:30–16:00 ET)

• Types: market, limit, stop, stop_limit, trailing_stop. [docs]
• Durations for a whole-share market, limit, stop, or stop-limit: day and gtc are marked yes. ioc, fok, opg, and cls are marked yes with a star. The orders page says to contact sales for any duration marked with a star. Do not send a starred duration unless the operator says this account has it. [docs]
• Default duration for a regular-session order is day.
• extended_hours true is what opts a limit into pre-market, after-hours, and overnight. Leave it false on a regular-session-only plan. A day order with it set can keep working after 16:00. [docs]
• Sub-penny prices are rejected. At or above $1.00, at most 2 decimal places. Below $1.00, at most 4. The reject text is invalid limit_price … sub-penny increment does not fulfill minimum pricing criteria (and the same shape for stop_price), code 42210000. [docs]

Stocks and ETFs, pre-market (04:00–09:30) and after-hours (16:00–20:00)

• Limit only, with extended_hours true. Any other type is rejected. [docs]
• Send time_in_force day. The current orders page also lists gtc, and its extended-hours table marks a GTC limit as yes. [docs] The 24/5 page says GTC has to be turned on by Alpaca ("reach out to your Customer Success Manager to enable it"). [docs] An older orders page (v1.4.2) said day only, and its table marked GTC as no. [docs] This pack was not placed on paper. Do not send gtc with extended_hours true unless the operator says that enablement is on.
• ioc, fok, opg, and cls are no in the extended-hours table. [docs]
• Bracket orders: extended hours are not supported. extended_hours must be false or omitted. [docs] OTO follows the same requirements as bracket. [docs] The orders page does not state an extended-hours rule for OCO. Do not send OCO with extended_hours true.
• A trailing stop does not trigger outside regular hours. [docs]
• Orders that are not extended-hours eligible, submitted after 16:00 ET, are queued for the next trading day. [docs] That queue is not a fill. Don't send one and call it done.

Stocks and ETFs, overnight (20:00–04:00 ET, Sunday evening through Friday 04:00)

• The orders page lists overnight as 20:00–04:00 ET, Sunday to Friday, inside "full extended hours," using the same extended_hours flag. The create-order reference says that flag covers pre-market, after-hours, and overnight. [docs]
• Limit only. day or, only if Alpaca has enabled it, gtc. [docs]
• A day order placed in the overnight session stays working through the next pre-market, regular session, and after-hours, and cancels at 20:00 ET if it is still open. It is not an overnight-only order. Say that before you send. [docs]
• The asset needs overnight_tradable true on the assets endpoint. overnight_halted true means a halt. The 24/5 page says a halted overnight order is accepted with status accepted and held. Do not send into a halt. [docs]
• The 24/5 page also says overnight trading is enabled by contacting Alpaca. The orders page says full extended hours are supported. [docs] Both are on the docs. Do not send an overnight order until the operator says this account has overnight turned on.
• Friday 20:00 ET through Sunday 20:00 ET is closed. A full-day holiday skips the overnight session that comes just before it. A half-day still runs the overnight session; after-hours may not. Read the calendar. Do not guess the holiday. [docs]
• Day-trading buying power does not apply overnight. The page says 2x is the max margin buying power in that session. [docs]

Stocks and ETFs, closed (weekend outside that overnight window)

• Nothing executes. Do not send. A non-extended day order submitted after the close is queued for the next trading day, which is a different order than the one the plan asked for. [docs]

Fractional and notional (stocks and ETFs)

• You pass qty or notional, not both. Both is HTTP 400. Each field allows up to 9 decimal places. [docs]
• The fractional page says market, limit, stop, and stop-limit, with time_in_force day. Not every symbol is fractionable. Read fractionable on the asset. If it is false, the reject text is requested asset is not fractionable. [docs]
• The same page says the floor is "as little as $1" of a fractionable name. It does not show a reject string for a smaller amount. [docs]
• Fractional sells are marked long. A fractional order cannot open a short. [docs]
• The body of that page says limit orders, including extended hours and overnight, work for fractional and notional the same way as whole shares. The closing note on the same page says fractional shares can only be bought or sold with market orders during normal market hours. [docs] This pack was not placed on paper. Do not send a fractional or notional order outside the regular session until the operator has seen which sentence the paper host enforces.
• A notional order cannot be replaced. Cancel it and send a new one. [docs]
• Notional is not allowed on options. The reject text is notional orders are not supported for options trading. [docs]

Equity options

• Regular session only. extended_hours must be false or omitted. The reject text is extended hours is not supported for options trading. [docs]
• Durations: day and gtc. Anything else fails invalid option time_in_force or order_time_in_force provided not supported for options trading. [docs]
• Single-leg types: market, limit, stop, stop_limit. Multi-leg (order_class mleg): market and limit only. [docs]
• qty is a whole number. qty must be integer for options trading. [docs]
• Market orders on options are only allowed during market hours. [docs]
• No trailing stop on the options type list. [docs]
• The options overview's short supported list says time in force day, and market and limit only. The placing-an-order section says day or gtc, and market, limit, stop, or stop_limit for a single leg. docs docs This pack follows the placing section. Do not send a type or duration that section does not list.
• There is no stock-style post-market for options on these pages.

Crypto

• 24 hours, every day, including weekends. The equity clock does not apply. [docs]
• Symbol shape is BTC/USD. [docs]
• Types: market, limit, stop_limit. Not stop. Not trailing_stop. [docs]
• Durations, from the crypto orders table: market and limit allow gtc and ioc. stop_limit allows gtc only. day, fok, opg, and cls are no for every crypto type. [docs]
• Wash trade protection applies to crypto. A possible wash trade is HTTP 403. [docs]
• order_class is simple only. No bracket, OCO, or OTO. [docs]
• Fractional qty or notional is allowed. The asset carries min_order_size, min_trade_increment, and price_increment. Read them. Do not assume a penny. [docs]
• Not marginable, and not shortable. Buying power checked is non_marginable_buying_power. [docs]
• One order, buy or sell, must not exceed $200,000 notional. docs If this order has no notional and no limit you can multiply by the quantity, stop and price it before you send.

Order classes on stocks

• simple (or omitted), bracket, oco, oto. [docs]
• Bracket is an entry plus a take-profit limit and a stop-loss. order_class bracket, nested take_profit.limit_price, and stop_loss.stop_price. stop_loss.limit_price makes the stop a stop-limit. time_in_force is day or gtc. Extended hours must be false or omitted. If one order in the group is canceled, the others are canceled. A buy bracket needs the take-profit above the entry and the entry above the stop. A sell bracket is the reverse. The stop has to be at least $0.01 from the entry. Both prices are required. [docs]
• OCO is the two exits after the entry has already filled. order_class oco. type is limit. Same take-profit and stop-loss objects. [docs]
• OTO is the entry plus only one of the two exits. order_class oto. The orders page says the rest of the bracket rules apply, and that replacing an OTO is not supported yet. [docs]
• On an OCO or OTO the stop has to be at least $0.01 from the base price. For an OCO that base is the take-profit limit: a sell stop is at least $0.01 below it, and a buy stop is at least $0.01 above it. For a limit OTO the base is the entry limit, and the stop sits on the exit side of that entry. The orders page also counts the current price as a base for OCO, OTO, and bracket. This check does not see the current price. If the quote is inside $0.01 of the stop, stop and ask. [docs]

Changing an order

• Replace is PATCH on the order id. The response is a new order with a new id. The new order's replaces field is the old id. The old order's status becomes replaced. The id does not stay the same. [docs]
• The replace reference lists qty, time_in_force, limit_price, stop_price, trail, and a new client_order_id. client_order_id cannot be the only field you change. notional on a replace is only for an IPO indication, and a non-IPO notional order cannot be replaced at all. [docs]
• The reference does not list symbol, side, or type. Do not send those on a replace.
• Bracket and OCO replacement is documented for limit_price and stop_price. OTO replacement is not supported yet. A trailing stop's trail can be replaced before the stop is hit, and you cannot switch between trail_price and trail_percent. [docs]
• Multi-leg replace can come back replace mleg order is disabled. [docs]

GTC age

• Alpaca cancels GTC orders 90 days after creation. expires_at is on the order. The cancel job runs at 16:15 ET on that date. The order sits in pending_cancel until the venue cancels it. [docs]

Holidays and early closes are not fully specified for the regular session on the pages this pack used. Read GET /v2/calendar and the errors. Outside a normal weekday, stop and ask.

Confirm gaps

Alpaca's Trading API has no dry-run confirm. The place call is the send. These are the cases you must reject yourself, because the docs say the broker will accept them, queue them, or the docs disagree.

What the broker does catch, with the text from the docs:

• Both qty and notional: HTTP 400. [docs]
• Sub-penny: 42210000 and sub-penny increment does not fulfill minimum pricing criteria. [docs]
• A symbol that is not fractionable: requested asset is not fractionable. [docs]
• Options extended hours, notional, non-integer qty, and bad time in force: the 42210000 strings in the options error table. [docs]
• A duplicate client_order_id is rejected. [docs]
• Wash trade: HTTP 403. This check applies to crypto as well as equities. Bracket, OCO, and trailing stops are exceptions to that check. [docs]
• Buying power, including the short-sale buying-power check. [docs]

If a quote lookup fails, you do not have a price. Do not place.

Don't double-send

• A retry after a timeout can place the same order twice if the second call uses a new id.
• client_order_id is the server's dedupe key. Up to 128 characters. If you omit it, Alpaca generates one. If you send one, a second submit with the same id is rejected. [docs]
• Build it before the call, from the order's details plus the current clock minute, and store it in the log before you send. On a timeout, GET /v2/orders:by_client_order_id?client_order_id= on the same host. If that returns the order, do not send again. [docs]
• The MCP uses the same id. get_order_by_client_id is the lookup. Do not invent a second key.
• How long a used id stays reserved after the order is filled or canceled is not on the pages this pack used. Do not reuse one.

Buy and sell table

There is no separate short action. side is buy or sell. [docs] Options add position_intent. [docs] Crypto cannot be shorted. [docs] Futures are not in this pack.

• Read the position first. GET /v2/positions/{symbol}. The examples use qty. A missing position is a 404 on that call. [docs] If the payload does not tell you long from short, stop. Do not guess a sign on qty.
• sell with no long opens a short. It does not close a long, because there isn't one. The orders page shows a short as side sell on a symbol you do not hold long. [docs]
• sell larger than the long is not a close. Cut the quantity to the long, or stop.
• On an option, send position_intent. The enum is buy_to_open, buy_to_close, sell_to_open, sell_to_close. A mismatch returns position intent mismatch, inferred: …, specified: …. A multi-leg leg without it returns leg.{i} position intent is required. [docs]
• After the fill, read the position again. A close must show a smaller qty, or a 404. If the position grew the other way, stop.
• A cash-like account: accounts are opened as margin. Margin and shorting need $2,000 equity. multiplier 1 means buying power equals cash. shorting_enabled false means do not short. [docs]
• Before a stock short: shortable and easy_to_borrow on the asset, shorting_enabled on the account, whole shares, not fractional. If easy_to_borrow is false, stop. The pages this pack used do not describe a locate request.
• Close paper positions in the same session. A paper fill is a position on that account until you close it. [docs] It is still not a live fill.

Ticks and combos

• Stocks at or above $1.00: 0.01. Below $1.00: 0.0001. That is the sub-penny rule, not a quote field. [docs]
• Options: the contract payload has size. The example value is "100". Do not assume 100. Read size. [docs] The tick is not on the pages this pack used. Say the tick is unknown and do not guess.
• Crypto: read price_increment and min_trade_increment on the asset. The BTC/USD example shows price_increment "1". [docs]
• Where symbol details live: GET /v2/assets/{symbol} for a stock or crypto pair. GET /v2/options/contracts/{symbol_or_id} for a contract. The MCP tools are get_asset and get_option_contract. If the tool isn't there, say so.
• Combos: one order, order_class mleg, with legs. Price it before you send. A negative limit is not documented on the pages this pack used. Do not send a negative equity or crypto limit. For an option credit, stop and ask if the docs you are looking at don't show the sign.
• Don't price off a feed you aren't entitled to. Basic, which is the default on paper and on live, is real-time IEX for stocks and ETFs, and an indicative feed for options. Algo Trader Plus ($99 a month) is all US stock exchanges and OPRA. [docs] Historical stock bars default the feed query to sip. [docs] On Basic, pass feed=iex. A paper-only account is only entitled to IEX. [docs]
• IEX is not the consolidated tape. A limit priced off IEX can sit far from the NBBO. Say which feed you used.
• Overnight history uses feed=boats. feed=overnight returns an error. Those trades are indicative, and the trade prints are delayed 15 minutes. [docs]
• Basic historical equity and option data is limited to the latest 15 minutes. That is a query window, not a statement that the IEX quote is delayed. The real-time column still says IEX. [docs]
• Keep the quote time, bid, and ask with every order. If bid or ask is missing, do not invent them.

Reading status

• The place response is the order object, and its status may be new or accepted, not filled. accepted is common outside the regular session: received, not yet routed. [docs]
• Poll GET /v2/orders/{order_id} or the client-order-id lookup. The orders page says the streaming interface is the way to keep state if you are running all day. [docs] This pack did not open the streaming page, so do not invent the socket URL.
• Poll every few seconds, a handful of times, not in a tight loop.
• Statuses. Final means no further updates on that order id. [docs]

• You can cancel until the status is filled, canceled, or expired. [docs]
• A replace does not keep the order id. Match the log on client_order_id and on replaces. [docs]
• Bracket, OTO, and OCO orders can carry group_id and group_role. Alpaca's changelog of 2026-10-08 adds both as optional fields on Order and OrderLeg. group_id is an opaque UUID shared by every order in the same bracket, OTO, or OCO, including legs and replacements. group_role is entry, take_profit, or stop_loss. For an OCO, the top-level order is take_profit. Both keys are omitted when the order is not in a bracket, OTO, or OCO. docs Use group_id and group_role to match legs and replacements.
• Paper is not live. Paper fills when the order is marketable against the NBBO, and it does not check your size against the NBBO size. When a fill is allowed, paper partial-fills a random size 10% of the time. Paper does not model queue position, your own market impact, slippage from latency, price improvement, regulatory fees, or dividends. [docs] Live can reject for buying power and for wash trades the paper account will also check. Wash-trade protection does run on paper, including crypto. [docs]

Failures

The equity/order ratio control restricts an account to closing orders when a position is 600% of equity, until Alpaca reviews it. Do not try to open a new position into that restriction. [docs]

Going live

1. The operator turns live trading on. You don't.
2. Use the live key and https://api.alpaca.markets. Read GET /v2/account on that host and bind the account it returns. [docs]
3. On the MCP, ALPACA_PAPER_TRADE=false is the live switch, and only with the live keys. [docs]
4. Rehearse that exact order shape on paper first.
5. Live-only differences the paper page names: market impact, queue position, latency slippage, price improvement, fees, dividends, and borrow fees (borrow fees are marked coming soon on paper). [docs] A paper accept is not proof live will accept.
6. If the host or the rules will not send live orders, write a ticket a person can place: account type (paper or live), symbol, side, position intent if it is an option, quantity or notional, order type, limit or stop, time in force, extended_hours, order class, the quote time, the feed, the bid, and the ask.

Permissions

• Option levels. [docs]

| Level | Allows | |---|---| | 0 | Options off | | 1 | Covered call, cash-secured put | | 2 | Adds long calls and long puts | | 3 | Adds call spreads and put spreads |

Paper has options on by default. Live approval is a separate request, and the options page says a level upgrade on a live account is not the same call. options_trading_level is never above options_approved_level. A paper accept is not proof live will accept. [docs]

• A level miss returns account not eligible for level2 options trading (the digit changes) or account not eligible to trade options. [docs]
• Pattern day trader. Alpaca's changelog of 2026-06-03 says the Trading API fields daytrade_count, daytrading_buying_power, and dtbp_check are deprecated and will be removed on 2026-07-06. docs Alpaca's intraday-margin page says the $25,000 equity threshold and the four-trades-in-five-days count are eliminated, and that a 12-month interim transition period will commence. During that window a firm may apply either the legacy rules or the new intraday margin rules. docs FINRA Regulatory Notice 26-10 says the same elimination, and that members may phase in over 18 months, until October 20, 2027. docs The two pages disagree on the length of the phase-in. Do not enforce a $25,000 day-trade gate. If the account payload still contains pattern_day_trader or daytrade_count, stop and ask. Do not count day trades yourself.
• In the money by $0.01 or more, a long option is auto-exercised if the account can support it. If it cannot, Alpaca can sell the position out within one hour of expiry. [docs] Do not hold a paper option through expiry to learn how live behaves. Exercise requests submitted between the close and midnight are rejected. [docs]

Symbols

• Stock or ETF: uppercase ticker, for example SPY. Asset class us_equity. [docs]
• Option: OCC, for example AAPL240119C00100000. Root, YYMMDD, C or P, then the strike times 1000 as 8 digits. The contract page shows that call as strike "100". A 0.50 strike shows up as 00000500 in the samples. [docs] Do not put a space in it.
• Crypto: BTC/USD, with the slash. [docs]
• Futures: not in this pack. Stop.
• Unknown fields are rejected often enough that the options page lists them one by one. Send only the documented ones. [docs]

Token and call costs

• One supervised round trip is a position read, a quote, validate_order, the place, a poll, and a position read. That is the API path. The MCP path is the same number of tool calls, with different names.
• GET /v2/orders without a tight filter gets heavier through the day. Ask for the symbol, or for the client order id.
• This pack outranks the MCP server's example prompts ("Buy 10 shares of AAPL at market"). Those examples are not permission to pick a size or a symbol.
• Stream order updates instead of polling when the session runs all day. The orders page recommends the streaming interface. [docs] The socket URL is not copied here.
• Rate limits. [docs]
  • Basic market-data historical calls: 200 a minute. Algo Trader Plus: 10,000 a minute. Websocket symbol caps are 30 (Basic equities) and 200 option quotes.
  • The Trading API clock documents a per-minute budget in X-RateLimit-Limit, with X-RateLimit-Remaining and X-RateLimit-Reset. The schema's sample value is an example, not your account's number. Read the header.
  • The Broker API rate-limit page is a different product. Do not copy a correspondent limit onto this Trading API account.
  • The MCP page says the API has per-account rate limits and does not give the number.
• On a 429, wait for X-RateLimit-Reset if the header is present, retry once, then stop.

Crash recovery

1. Read open orders, today's orders, and positions on the same host you were using.
2. Match them to your log by client_order_id, then by order id. On a bracket, OTO, or OCO, also match legs and replacements by group_id and group_role. docs Log columns: time (US Eastern), host (paper or live), symbol, side, position intent, quantity or notional, type, limit, stop, time in force, extended_hours, client_order_id, order id, group_id, group_role, status, feed, bid, ask.
3. An order that is not in your log is not yours to cancel. It may be another session's.
4. There is a client-tag field. It is client_order_id. Look it up with GET /v2/orders:by_client_order_id?client_order_id= before you decide an unlogged order is someone else's. [docs] If you find one of yours that never got a log line, log it, then decide.

Order playbook

Run validate_order before step 6. If ok is false, do not send. Fetch rules.json and validate_order.py into the same folder. Tests are test_validate_order.py.

1. Read the clock (US Eastern) and name the session. Crypto skips the equity session.
2. Read the position for the symbol, then pick the side and, for an option, the position_intent from the table.
3. Get a fresh quote on a feed this account is entitled to. Basic means feed=iex for a stock. Do not default the data call to sip.
4. Build the order and check it:
   • type and time_in_force against the session and the asset
   • extended_hours true only for a stock limit with day, and only when the plan is outside the regular session or the plan says so
   • the tick, or an explicit "tick unknown" stop
   • quantity against the position and the desk limits
   • uppercase symbol, slash on crypto, OCC on an option
   • client_order_id already chosen, 1 to 128 characters, not reused
5. Check open orders and the log for that same id, and for the same symbol and side in the last 15 minutes.
6. There is no confirm call. validate_order is the check. Then place.
   • Paper: POST /v2/orders on https://paper-api.alpaca.markets.
   • MCP: the place tool for that asset, with ALPACA_PAPER_TRADE still true.
7. Read the order back by client_order_id until the status is final, or until you have polled a handful of times. new and accepted are not fills. partially_filled is not done.
8. Re-read the position. On a close, qty must shrink or the position must 404. It must not flip.
9. Log it with the quote time, the feed, the bid, and the ask.
10. To change the price, replace it. The new id comes back on the replace, and replaces points at the old one. To change a notional order, or an OTO, cancel and resend. A replace can change time_in_force; cancel instead when you are not sure the new duration is legal for the session.

Paper round trip, one share, regular session. Post each body to POST /v2/orders on https://paper-api.alpaca.markets. Send the sell only after the buy is filled and the position is long 1. A resting buy plus a sell at or below that buy limit is a wash-trade 403, on equities and on crypto. [docs]

{
  "symbol": "SPY",
  "qty": "1",
  "side": "buy",
  "type": "limit",
  "time_in_force": "day",
  "limit_price": "100.00",
  "extended_hours": false,
  "client_order_id": "paper-spy-buy-20261016"
}

{
  "symbol": "SPY",
  "qty": "1",
  "side": "sell",
  "type": "limit",
  "time_in_force": "day",
  "limit_price": "100.00",
  "extended_hours": false,
  "client_order_id": "paper-spy-sell-20261016"
}

Don't know: stop and ask

• Whether paper accepts gtc with extended_hours true on an account that has not had GTC extended hours enabled.
• Whether a fractional or notional limit outside the regular session is accepted. The fractional page says both yes and no.
• Whether OCO with extended_hours true is rejected. Bracket says no. OCO doesn't say.
• The option tick, and the sign of a credit on a multi-leg limit.
• A locate workflow when easy_to_borrow is false.
• How long a client_order_id stays reserved after the order is gone.
• What status held means. It is on the enum. The orders page doesn't define it.
• The Trading API order-call budget. The clock documents the headers. The market-data page documents 200 a minute for historical calls. Neither page states an order-post budget.
• The websocket URL and the auth frame.
• Holidays and early closes for the regular equity session, beyond the overnight calendar notes.
• Futures, fixed income, and IPO order handling, other than "an IPO is limit-only until the first trade, and the asset carries an ipo attribute." [docs]
• Whether a paper options fill, exercise, or assignment matches live. Paper non-trade activities show up the next day. Balances and positions update immediately. [docs]
• Which rule this account is under if pattern_day_trader or daytrade_count is still on the payload after 2026-07-06.
• Exchange overnight trading starting 2026-12-06, pending SEC approval. An 8:00 to 9:00 p.m. ET pause Monday through Thursday, with the trade date rolling at 8:00 p.m. ET. During that pause, orders that would route to exchanges for the overnight session are cancelled on the exchange path and re-routed to overnight ATSs where those venues are operational. docs Re-check on 2026-12-07. Do not send against that session until it is confirmed.

Look it up

Fetched 2026-10-16. Re-checked 2026-10-20 for the pattern-day-trader lines, the group_id and group_role fields, the 2026-12-06 overnight note, the crypto $200,000 order cap, and the OCO stop distance. Prefer the unversioned page when an older /v1.4.2/ or /v1.1/ copy disagrees.

• Trading API overview: https://docs.alpaca.markets/us/docs/trading-api
• Create an order (types, time in force, extended_hours, position_intent): https://docs.alpaca.markets/us/reference/postorder
• Placing orders (sessions, brackets, OCO, OTO, trailing stops, fractional tables, statuses): https://docs.alpaca.markets/us/docs/orders-at-alpaca
• Working with orders (client_order_id, shorts): https://docs.alpaca.markets/us/docs/working-with-orders
• Get order by client order id: https://docs.alpaca.markets/us/reference/getorderbyclientorderid
• Replace an order: https://docs.alpaca.markets/us/reference/patchorderbyorderid-1
• Paper versus live: https://docs.alpaca.markets/us/docs/paper-trading
• Clock: https://docs.alpaca.markets/us/reference/legacyclock
• Account flags: https://docs.alpaca.markets/us/docs/account-plans
• Positions: https://docs.alpaca.markets/us/docs/working-with-positions
• Fractional trading: https://docs.alpaca.markets/us/docs/fractional-trading
• 24/5 overnight: https://docs.alpaca.markets/us/docs/245-trading
• Crypto: https://docs.alpaca.markets/us/docs/crypto-trading
• Options (Trading API): https://docs.alpaca.markets/us/docs/options-trading
• Options levels and error strings: https://docs.alpaca.markets/us/docs/options-trading-overview
• Market data, IEX versus the full tape: https://docs.alpaca.markets/us/docs/about-market-data-api
• Historical bars feed values: https://docs.alpaca.markets/us/reference/stockbars
• Auth headers: https://docs.alpaca.markets/us/docs/authentication
• User protection (wash trades, 600% equity check): https://docs.alpaca.markets/us/docs/user-protection
• End of the pattern-day-trader rule (Alpaca says a 12-month interim): https://docs.alpaca.markets/us/docs/understanding-finras-new-intraday-margin-rule-and-the-end-of-pdt
• FINRA Regulatory Notice 26-10 (18-month phase-in until October 20, 2027): https://www.finra.org/rules-guidance/notices/26-10
• PDT field removal, 2026-07-06: https://docs.alpaca.markets/us/changelog/2026-06-03-pdt-651df23
• Order group_id and group_role, 2026-10-08: https://docs.alpaca.markets/us/changelog/2026-10-08-order-group-db02af7.md
• MCP: https://docs.alpaca.markets/us/docs/alpaca-mcp-server
• Idempotent client_order_id on the official CLI: https://docs.alpaca.markets/us/docs/alpacas-cli

The Broker API rate-limit page is not a source for this pack. This pack is the Trading API.