If you’ve ever asked what is a sideboard in MTG, here’s the short answer first: in most Constructed formats, a sideboard is a separate set of up to 15 cards you can swap into your main deck between games of a match. It exists so your deck can adapt to what your opponent is doing—bringing in narrow, high-impact answers or shifting your game plan after you see their strategy. That’s the official idea behind sideboards in Magic’s rules and tournament policies.

Below, we’ll break down the formal rules (Constructed vs. Limited, Arena vs. tabletop), show the point of a sideboard in real strategy terms, and map a clean, repeatable process to build and use yours well—without turning every match into a guess-fest.

The Rules, Plainly

Constructed (paper and digital)

In Constructed play, your sideboard may contain no more than 15 cards. Those cards are outside your game until sideboarding time, when you can modify your deck for the next game of the match. Card-count limits and duplication rules apply to the combined deck + sideboard. 

Limited (Draft/Sealed)

In Limited, your “sideboard” is effectively the rest of your card pool that didn’t make the maindeck (plus unlimited basics). Between games, you can reconfigure using any cards from that pool. It’s more flexible than Constructed and often underused by newer players. 

MTG Arena

Sideboarding exists in Best-of-3 on Arena. After Game 1, Arena gives you a timed sideboarding screen to swap cards before Game 2 and again before Game 3. In Best-of-1 ladders, there’s no sideboarding between games (some BO1 formats emulate “pre-boarded” metagames, but you don’t actually swap mid-match). 

Commander (EDH) note

Commander is a different beast: regular Commander doesn’t use sideboards. Wizards’ August 2025 update made this explicit in rules text. If you encounter sideboards in Commander, it’s a table or event variant, not the default. 

So… What’s the Point of a Sideboard in MTG?

Think of your maindeck as “best into the unknown.” Your sideboard lets you become “best into this opponent.” The goal is small, high-leverage improvements that raise your win rate post-board:

• You trim or cut cards that are weak in the matchup.
• You add cards that are excellent in the matchup—efficient interaction, hate pieces, haymakers, or threats that line up better.

Wizards’ classic sideboard primer puts it simply: you avoid “dead” cards and pack effects that matter when they matter (e.g., artifact/enchantment destruction against decks that actually have them). 

The Anatomy of a Good Sideboard (15 cards with jobs)

You don’t need 15 random “good cards.” You need roles. Here’s a clear way to think about it:

• Targeted interaction: two to four cards that efficiently answer a specific permanent type or axis (fast artifact decks, graveyards, swarm creatures, planeswalkers).
• Speed dials: a few cards that change your deck’s speed—either cheaper removal vs. aggro, or more resilient threats/engines vs. control.
• Mirror breakers: cards that are specifically strong in the mirror (threats that are hard to kill, or answers that trade up on mana).
• Plan pivots: sometimes you bring an alternate win condition that dodges the hate you expect.

The Sideboarding Process: A Simple Between-Games Script

You have only a couple of minutes between games. Use a repeatable mini-script so you don’t panic-swap.

• Name the matchup in one sentence. “They are Domain midrange with 8 sweepers,” “They’re Mono-Red Burn with 8+ one-drops,” “They’re artifact combo, light on creature removal.”
• Identify your role.  Are you the beatdown (must end the game quickly) or the control (must survive and go over the top)? Naming this determines what you cut and add.
• Cut true blanks and clunky overlaps.
   Remove the cards that literally do nothing (e.g., creature removal vs. control with few creatures) and trim redundant, slow effects that overlap.
  
• Add high-impact hits first.  Bring in the cards that directly address the opponent’s plan or shore up your weak point.
• Check your curve and threat count. Don’t sideboard yourself into a deck that can’t function. Keep your curve sensible and your clock real.
• Reality check. Does the swap align with your role? If you’re supposed to be faster now, your deck should actually be faster.

Constructed vs. Limited: Different Sideboarding Mindsets

In Constructed, your 15 are pre-chosen for a known metagame. You already know which cards come in for which common opponents, and your plan rarely changes by more than one or two cards per game.

In Limited, your entire unused pool is live. That means you can go far beyond “two cards in, two out.” You can re-build—going bigger against slow bombs, adding reach for fliers, or splashing a bomb color if the matchup’s speed allows. Newer players under-utilize this flexibility; the best Limited grinders don’t.

MTG Arena: Practical Tips for the Sideboard Screen

Arena’s Best-of-3 sideboarding is timed, so organize your sideboard by jobs in deckbuilding: graveyard hate together, removal upgrades together, anti-control package together. Then, in the sideboarding screen:

Common Mistakes (and better habits)

Over-boarding. Bringing in too many narrow cards dilutes your game plan. Target four to seven swaps in most Constructed matchups unless you’re fundamentally changing roles.

Adding answers that don’t line up on mana.  If their engine costs two, your three-mana answer may be too slow on the draw. Be honest about mana tempo.

Cutting all your win conditions.  Post-board, many decks increase interaction. You still need threat density to close; don’t sideboard into 52 answers and hope to topdeck a single finisher.

Ignoring play/draw differences. On the draw, you may need cheaper interaction; on the play, you can keep or add slightly greedier cards that snowball.

Example Matchup Thought Experiments

You don’t need specific card lists to practice good logic. Here are three simple “mental reps” you can adapt to your format:

1. Vs. artifact combo: Your plan: keep the battlefield honest and attack their engine. Bring in artifact hate and ways to interrupt their key spell. Cut slow, sorcery-speed fluff that doesn’t affect the stack or board early. (This is precisely where sideboards shine—narrow but devastating effects.)
   

2. Vs. Mono-Red aggro: Your plan: lower your curve, increase life-gain or efficient removal, shave card-draw engines that don’t stabilize the board. If your deck can swap in two-mana lifegain/removal that trades up, do it.

3. Vs. hard control: Your plan: become resilient. Trim dead creature removal; add must-answer threats, hand disruption, or un-counterable/recursive cards, depending on format.

Arena and Paper: How Sideboarding Differs in Feel

Arena is quick and ruthless; you have a clock and you don’t see body language or hear sighs when a card hits. That pushes you to pre-plan packages to avoid timeouts. 

Paper gives you tactile feedback and a real table—but you must sleeve your sideboard the same as your maindeck and follow tournament logistics cleanly. The official tournament rules and judge resources advise consistent sleeves and careful, timely swaps. 

Frequently asked questions

What is a sideboard in MTG?

A separate set of up to 15 cards you keep outside your main deck and can swap in between games of a match. In Limited, your unused pool functions as your sideboard. 

What is a sideboard in MTG Arena?

Exactly the same concept in Best-of-3: after Game 1 (and again before Game 3), Arena gives you a timed swap screen. There is no sideboarding in Best-of-1. 

What is the point of a sideboard in MTG?

To adapt: remove cards that are weak in the matchup and bring in targeted cards that are strong against your opponent’s strategy. Wizards’ primer highlights classic examples like enchantment/artifact hate that you don’t want main deck but love in the right matchup.

How many cards can be in a sideboard?

In Constructed, up to 15. In Limited, all unused pool cards (plus unlimited basics). Combined deck + sideboard must still follow card-copy limits where applicable. 

Does Commander use a sideboard?

No—regular Commander does not use sideboards; Wizards clarified this explicitly in 2025. House variants exist, but they’re not default rules.

A Quick History Pointer (for the curious)

You’ll see sideboards described in rules and in community wikis the same way: a set of additional cards you can use to modify your deck between games. Even older pages anchor the 15-card cap and the “outside the game” phrasing, while modern tournament documents keep that definition concise. If you’re chasing citations, both the MTG Wiki and the Magic Tournament Rules align on these essentials.

Wrap-Up

A sideboard in Magic: The Gathering is the most efficient way to pivot your plan after you learn what the opponent is doing. In Constructed, it’s up to 15 cards; in Limited, it’s the rest of your pool. In Arena, you sideboard in Best-of-3 via a timed screen; in Commander, there’s no sideboard by default. Use roles (“jobs”) to build your sideboard, a short script to sideboard quickly and coherently, and you’ll see your post-board win rate climb.

If you’re planning a living-room play space for those long Best-of-3 nights, a balanced, low coffee table makes a surprisingly good “game board” height—browse ideas and proportions in our coffee tables category when you’re ready to set the scene for your next match.