MTG Sideboard Guide: How to Build and Use Your 15 Cards
August 6, 2026
What this MTG sideboard guide covers
A good MTG sideboard guide should leave you with more than theory. It should leave you with an actual 15 cards and a plan for when each one comes in. In constructed Magic, your sideboard can hold up to 15 cards, and you don't have to swap 1:1: your deck just needs to stay at 60 cards or more, and your sideboard at 15 or fewer (Magic Tournament Rules 3.16).
That flexibility is also where players get lost. Fifteen slots sound generous until you are trying to answer six different archetypes with them. This guide breaks the sideboard into the jobs its cards actually do, shows you how many cards to move per matchup, and gives you a template for writing the plan down before you are stuck figuring it out at the table.
Sideboarding only exists between games of a match
Sideboarding happens between games one, two, and three of a best-of-three match, once you have seen what your opponent is playing. In a best-of-one match there is no game two, so there is nothing to sideboard into. MTG Arena gives Bo1 decks a separate seven-card "sideboard," but it exists only for cards that reference effects outside the game, like Learn, not for matchup-based swaps.
This matters because it changes what "sideboard guide" even means depending on where you play. If you are grinding Bo1 ladder, your fifteen (or seven) cards need to be relevant from the opening hand of the only game you get. If you are playing a paper tournament or a best-of-three Pioneer, Modern, or Standard event, everything below applies in full.
Start with your own deck, not your opponent's list
The instinct is to build a sideboard around your opponent's cards. Better to start with your own deck's game one weaknesses. Ask what beats you when your draw is fine and your opponent's isn't. Fast aggressive starts? Graveyard-based value engines? A single removal spell that answers your whole plan? Those weaknesses point straight at what your sideboard needs to cover, and they matter more than any specific opposing decklist because they show up against several archetypes at once.
Once you know your own soft spots, look at the cards already in your 60 that do the least work against them. Those are your cuts. A sideboard plan is really two plans in one: what comes in, and what makes room for it. Players who only think about the first half end up bloating their curve or diluting their win conditions in game two, which is how a tuned 75 turns into an unfocused pile.
The four jobs a sideboard card can do
Every card you consider for the fifteen should earn its slot by doing one of these jobs well. Cards that don't fit any of them usually belong in the maindeck or nowhere at all.
| Category | What it does | Example |
|---|---|---|
| Hate cards | Narrow, high-impact answers to one strategy. Excellent when relevant, close to dead otherwise. | Rest in Peace exiles all graveyards on entry and keeps exiling anything that would go there, which is brutal against reanimator or graveyard value decks and does nothing against a pure aggro deck. |
| Flex answers | Broad interaction that is fine across many matchups, not spectacular in any single one. | Generic removal or a catch-all counterspell that trades with almost anything your opponent plays. |
| Plan-B cards | A different route to winning when your normal plan is too slow or too fragile for a matchup. | A bigger threat or an alternate win condition brought in against decks that outgrind your main plan. |
| Maindeck upgrades | Cards that are simply better against the field than what they replace, once you know what the field looks like. | Veil of Summer gives hexproof from blue and black and can't be countered, so it upgrades hard against blue or black-heavy fields and is a clean cut against a mono-red opponent. |
Cards like Alpine Moon (shuts off one nonbasic land's abilities) or Damping Sphere (taxes multi-spell turns and caps land mana) are textbook hate cards: excellent against the one thing they answer, close to a blank everywhere else. Build your fifteen with a mix, not fifteen copies of the same job.
How many cards to actually swap
Most matchups call for three to six card swaps, not a full overhaul. Bring in too few and you barely notice the difference in game two. Bring in too many and you have built a second deck you never playtested, with a curve and mana base that no longer match. If a single matchup genuinely needs eight or more changes, that usually means your maindeck plan does not survive contact with that archetype at all, which is a maindeck problem more than a sideboard one.
- Close, favorable matchups: 1 to 3 swaps, mostly trimming a dead card or two.
- Typical adversarial matchups: 3 to 6 swaps, your normal sideboarding plan.
- Bad matchups you are trying to steal games in: 6 to 8 swaps, sometimes a real plan-B.
Write the plan before round one, not during it
The best sideboarding decisions happen at your kitchen table with a laptop open, not across from an opponent with a clock running. Before an event, write out your in and out list for every archetype you expect to face. A simple table works:
| Matchup | Cards in | Cards out | Why |
|---|---|---|---|
| vs. Aggro | Lifegain / cheap sweeper | Slow card advantage spells | You need to survive before you can out-value them |
| vs. Control | Extra threats / discard | Narrow removal for creatures they don't play | Removal is dead against a deck with few creatures |
| vs. Graveyard combo | Graveyard hate | Situational sideboard cards for other matchups | One turn of exiled graveyard can end their whole plan |
Fill this in with your own archetypes and cards rather than borrowing someone else's list wholesale. If you are still settling your maindeck 60, our guide to building an MTG deck covers curve and mana base decisions that will shape which sideboard cards you actually need. Once your swaps are set, double-check they keep the deck format-legal, since a card that is fine in Modern can be banned in Pioneer or Standard. Saving the finished plan as deck notes means you can pull it up on your phone between rounds instead of rebuilding it from memory.
Common sideboarding mistakes that cost matches
Sideboarding badly is often worse than not sideboarding at all, because you have spent your fifteen best minutes weakening your own deck. Watch for these:
- Boarding for game one's list, not game two's. Your opponent sideboards too. Expect their answers to your deck, not a repeat of the game you just played.
- Cutting your win conditions to fit in answers. A sideboard plan that removes your way of actually winning just delays the loss.
- Ignoring play versus draw. On the draw you can afford a slightly slower, more reactive configuration; on the play, lean into pressure and keep your curve low.
- Sideboarding the same way every round. A plan written for the "expected" version of an archetype can be wrong against the specific 75 you are actually facing. Adjust when you see something unusual in game one.
Frequently asked questions
How many cards can you put in a Magic sideboard?
In constructed formats your sideboard can hold up to 15 cards. There is no minimum, and you don't have to swap cards one for one anymore: you can bring in any number of cards between games as long as your final deck has at least 60 cards and your sideboard has 15 or fewer, per Magic Tournament Rules 3.16.
How many cards should you actually sideboard in per matchup?
Most matchups call for three to six card swaps. Fewer than that and the change barely registers; more than that and you risk turning a tuned deck into an untested pile with a broken curve. Matchups that need eight or more swaps usually point to a weakness in the maindeck plan itself.
Can you sideboard in a best-of-one match?
No. Sideboarding happens between games of a match, and a best-of-one match only has one game. MTG Arena gives Bo1 decks a separate seven-card pool, but it exists only for effects that reference cards "outside the game," like Learn, not for matchup-based swaps the way Bo3 sideboarding works.
Do you have to swap sideboard cards one for one?
No. That restriction used to exist but was removed years ago. You can bring in two cards and take out four, or vice versa, as long as your deck stays at 60 cards or more and your sideboard stays at 15 cards or fewer after the swap.
What's the difference between a hate card and a flex sideboard card?
A hate card is narrow and powerful against one specific strategy, like graveyard hate against reanimator decks, but weak or dead elsewhere. A flex card, such as generic removal, does reasonable work across many matchups at once. Strong sideboards mix both so you have sharp answers for your worst matchups and broad ones for everything else.
Next step: turn theory into your fifteen
Pick your three worst matchups, name the specific cards or effects that beat you, and write down the swap for each one before your next event. That short exercise, repeated a few times, is what turns a random pile of sideboard cards into an actual plan. If you want somewhere to keep that plan attached to the deck itself, our rundown of MTG deck building tools covers a few options for storing notes alongside your list so they travel with you round to round.