Parlay Builder

A small website where a group of friends picks NFL games each week. It finds the plays most of you agree on and builds a few parlays out of them.

• Weekly schedule and FanDuel lines from The Odds API (free key). The week runs Tuesday to Tuesday, so Thursday, Sunday, and Monday games are all included. ESPN is a backup for the schedule.

• Players: Daniel, Asher, and Matt (set with PLAYERS). Pick your name and the site remembers you on that device.

• My Picks: tap a spread, total, or moneyline to select it, tap again to remove it. Picks stay private until you hit Submit, which saves them at FanDuel's line at that moment. Tap Edit picks to change them later: your submitted picks keep counting until you resubmit, bets you keep stay at the line you got, and picks on games that started can't change. Only your own picks show here, so nobody copies anybody. After submitting, Copy picks copies a plain-text list of that day's picks (like KC -3.5, GB/DET O 49.5, JAX ML, one per line) for a group chat. Clear my picks (next to your name) wipes your picks for the week, except games already under way.

• Completed games: live games stay at the top of the Picks tab (marked Live); once a game is over it moves to a grayed-out Completed games section at the bottom, with the final score for games anyone bet on. Once the score is in, your picks there turn green ✓ (won), red ✗ (lost), or gray P (push), and where you lost, the side that won gets a dashed green outline. The Bet Slip does the same for settled parlays.

• Build a parlay (switch at the top of the Picks tab): tap any bets to see what a one-off parlay would pay at FanDuel's current lines for any stake. Nothing in it is saved or shared until you Post. Legs from the same game are fine (say the Over plus Packers -6.5), except the spread and moneyline together; FanDuel prices those as a Same Game Parlay, so the app flags that its payout will differ and to enter FanDuel's when placing it.

• Group Board: every submitted bet ranked by how many of you took it, plus who still needs to submit. It flags bets where FanDuel's line has moved since.

• Parlays: custom parlays first, then up to five suggested parlays built from the majority picks. Once any game in a parlay with money on it kicks off, it moves to In play (✓/✗ on legs as they finish), and once it's decided, to a grayed Completed section marked Won (with the payout), Lost, or Push. Every parlay on the Bet Slip is always somewhere on this tab. Each shows the price, the payout for your stake, a rough chance of hitting, and a list of bets that are one vote short. Everyone types in how much they want on the parlays they like; one with money from a majority of the group is marked Group's pick.

• Stats: season money per person (staked, paid back, net), the group's parlay record, everyone's pick records (by spread, total, and moneyline), how the group's consensus picks have done, and a week-by-week history. Games are graded automatically from ESPN's final scores (free), about 3 hours after kickoff.

• Likes and dislikes (Parlays tab): 👍 or 👎 a parlay (tap again to clear, or tap the other to switch) and 👎 any leg you don't trust; small initial circles show who. Money on a parlay counts as a like, and a parlay a majority likes is the Group's pick.

• Copy & edit: opens any open parlay in Build a parlay with its legs filled in. Each leg shows its win chance, a swap to the same team the other way (spread vs. moneyline), and Drop, each with the parlay's new hit chance and payout. Posting makes a new custom parlay "based on" the original, which stays as it was.

• Research: pick any team for its season so far, from ESPN's scoreboard (free): record (home/away, streak, last 5, points per game), against the spread (overall, as favorite/underdog, home/away), over/under, strength of schedule (opponents' win %, ranked), and a game log with each line and result. Lines come from ESPN's odds, or the saved FanDuel line when ESPN has none. A Team | League switch adds a league view: how favorites, underdogs, home and road teams, and overs are doing, plus every team ranked against the spread and on over/unders (tap one to open its page). Finished weeks are cached; weeks in progress re-check every 15 minutes during games, else every 6 hours.

• Analysis: each of your open picks with its win chance (FanDuel's odds on both sides with the house's cut removed) and the other way to bet the same team (spread vs. moneyline); live parlays' hit chances and weakest leg; close calls (how far lost picks missed and whether the other bet would have won); parlays that lost by one leg; and parlays vs. the same money as straight bets. Lines are kept for past weeks people bet on so look-backs can show prices.

• Custom parlays (Parlays tab, + Build your own): pick any bets in the Build a parlay view, set your stake, and Post. It shows up as "Daniel's Parlay 1" (then 2, ...) for the others to join with their own stakes, and flows into the Bet Slip and Stats like the group parlays. One bet posts as a straight bet; same-game legs follow the rule above. It closes to new money once any of its games starts. If everyone pulls out, it disappears. Every parlay card (here and on the Bet Slip) has a Copy button that copies its legs, one per line, then the odds, what $10 pays, and the total bet and payout if anyone is in.

• Bet Slip: for whoever places the bets. Every parlay with money on it, its legs and odds, each person's stake and payout, and a "who owes what" total. A parlay is saved as it was when people bought in, so it stays on the slip after kickoff or if picks change (it gets flagged if it's no longer a current option). Legs flag any line FanDuel has moved since. Mark placed asks for the total payout FanDuel shows (pre-filled with the site's estimate), records who placed it and when, moves it below the ones still to place, and locks its stakes so the slip keeps matching the real bet (Undo unlocks). From then on the real payout is used everywhere: each person's winnings, the odds shown, copied text, and season Stats. Edit payout fixes a typo. Once a parlay wins (or pushes), Mark paid out records that everyone's been paid; until then the slip's summary shows To pay out with what each person is owed.

• NFL | CFB (switch under the week): flips the whole site to college football and back. College covers games with a Power 5 team (ACC, Big 12, Big Ten, SEC, Pac-12, by ESPN's conference list) and works like the NFL side: picks, Board, Parlays, Bet Slip, Bet Stats, Analysis, and CFB Stats/Data, with its own picks, parlays, and history. Its weeks are numbered one ahead of the NFL's (college Week 9 is NFL Week 8). Differences: no player props (a credit per game adds up fast with ~35 games), no injury card (ESPN has almost no college injury reports), and the extra manual refreshes and higher credit limit fall on Saturdays. Teams are matched by full name, since college nicknames repeat. Locally its data is in data/cfb.json (CFB_DATA_FILE); hosted, in the Redis key parlay:cfb.

Run it

npm install
npm start            # http://localhost:3000

To pull FanDuel lines, get a free key at https://the-odds-api.com, then:

cp .env.example .env
open -e .env         # macOS; paste your key after ODDS_API_KEY=, save, close
npm start

The startup message should say Using FanDuel lines from The Odds API. .env is git-ignored, so the key never gets committed.

If no schedule source can be reached, it shows a demo slate and retries every 5 minutes. The terminal prints why each source failed.

Settings (in .env or as environment variables):

Variable	Default	What it does
ODDS_API_KEY	(empty)	The Odds API key. Needed for lines, so picks need it too
PLAYERS	Daniel,Asher,Matt	Who's in the group, comma-separated
BOOKMAKER	fanduel	Book to pull lines from (draftkings, betmgm, williamhill_us, ...)
DAILY_CREDIT_LIMIT	16	Backstop: most credits line refreshes can spend per day (Eastern)
SUNDAY_CREDIT_LIMIT	30	The same, on Sundays
LOGINS	(empty)	Turns on the login page: matt:pass,daniel:pass,asher:pass (usernames match players). Set it in Vercel, not in the repo
SESSION_SECRET	(from LOGINS)	Optional key that signs login sessions (60 days)
GROUP_CODE	(empty)	Optional shared code friends enter before they can use the site
SEASON_START	Tuesday after Labor Day	Sets the "Week N" label (YYYY-MM-DD, a Tuesday)
PORT	3000
DATA_FILE	data/db.json	Where players, picks, and the schedule are saved

API credits

The free tier has 500 credits a month. The schedule, team records, and final scores (from ESPN) don't use any. FanDuel lines cost 3 credits per refresh (spreads, totals, and moneylines).

Player props cost 1 credit per market per game: anytime TD + passing TDs is 2 a game, about 28-32 for a full slate.

Lines update at 11 AM and 6 PM Eastern: the first visit after each time pulls fresh lines once (3 credits), and everyone shares them. A new week with no lines yet gets them on its first visit. Sundays add 2 manual refreshes (the ↻ Refresh button only shows then) for late injury news.

Props update Thursday and Sunday at 11 AM Eastern, for games that haven't started. They pause if the month's credits left would drop under 75, so lines keep working to the end of the month. Games that come back with no props (often night games, posted later) are checked again every 3 hours until kickoff; a check that finds nothing costs nothing.

	Lines	Props	Per week
Tue, Wed, Fri, Sat, Mon	2 × 3 = 6	0	30
Thu	6	~32	~38
Sun	6-12	~30	~36-42
Week	42-48	~62	~104-110

College lines cost the same 3 credits a refresh, on the same 11 AM / 6 PM schedule, so they add up to about 180 a month. With both leagues on, that goes past the free 500 in a heavy month; NFL props pause first (they stop at 75 credits left), which keeps lines for both working. A league's lines only refresh when someone opens that league, so a quiet week costs less.

NFL alone is roughly 450-470 a month in the worst case (a refresh only happens if someone visits), under the free 500. DAILY_CREDIT_LIMIT and SUNDAY_CREDIT_LIMIT are a backstop for line refreshes only. Once every game of the week has kicked off, nothing refreshes until the next week. The Picks tab shows when lines and props were last updated, when they update next, and credits left this month.

Props are graded from ESPN's box scores (free): anytime TD counts every touchdown the player scores (not ones he throws), and a player who doesn't play is a push, like a void at the sportsbook.

How the parlays are built

1. Voters are friends who submitted picks this week.
2. A bet counts as consensus if more than half the voters picked the same side of it. With 1 or 2 voters, everyone has to agree. Picks with slightly different lines (submitted at different times) still count together, and the parlay uses the most common line.
3. Each game contributes only its most-picked consensus bet. Books won't let you parlay both sides of a game, and most limit same-game combos in regular parlays.
4. Games that have already kicked off are left out.
5. From that pool it builds, skipping duplicates:
   • Everybody Agrees: every bet all voters picked
   • Crowd Favorites: the top 3 by votes
   • Safest Majority: the bets most likely to hit
   • Plus-Money Swing: the bets with the biggest payouts
   • Full Send: every consensus bet

Parlays are priced at the lines each pick was submitted at, which can drift from FanDuel's current lines. The board and parlay cards flag any that moved. "Hit chance" strips a typical ~4.5% book margin from those odds, so it's an estimate. Expected return is almost always negative because the book's edge compounds on every leg.

Week to week

The week flips every Tuesday at 6 AM Eastern: new games, fresh lines, and empty picks. Nothing is deleted. Past weeks stay in the data and show up on the Stats tab with their results.

Hosting on Vercel (free)

Vercel runs the site for free but has no lasting disk, so the data goes in a free Upstash Redis database you add from Vercel's dashboard. (Locally, the site keeps using data/db.json.)

1. Sign in at https://vercel.com with GitHub (the free Hobby plan).
2. Add New → Project, import this repo, and leave the build settings alone (vercel.json handles them).
3. Under Environment Variables, add ODDS_API_KEY. Strongly consider GROUP_CODE too: the site will be on the public internet. Add PLAYERS if the group changes.
4. Click Deploy. The page loads, but picks won't work until step 5.
5. In the project, open Storage → Create Database → Upstash for Redis (free plan) and connect it to the project. That adds KV_REST_API_URL and KV_REST_API_TOKEN for you.
6. Deployments → ⋯ → Redeploy so the site picks up the database.
7. Optional, to bring over picks and history from your computer: put the KV_REST_API_URL and KV_REST_API_TOKEN values in your local .env, then run npm run upload-data.

Pushing to the repo's default branch redeploys automatically.

You can also host it anywhere that runs Node: npm start with the same environment variables. Without Upstash variables it uses data/db.json, so use a persistent disk.

Tests

npm test