MTG on Cockatrice: Free Testing, and What It Cannot Do

What Cockatrice actually is

Cockatrice is a free, open source program that simulates a table. Two or more people connect to a server, load decks, and move cards around.

The critical design decision: it enforces no rules whatsoever.

It will move a card from your hand to the battlefield. It will not check whether you had the mana. It will let you attack with a creature you played this turn. It will let you draw eight cards. It tracks life totals and counters because you told it to, not because it understands why.

Everything is manual, and every legality check is done by the humans playing.

Why that is a feature, not a bug

The instinctive reaction is that a client which does not enforce rules is a broken client. For its actual purpose, the opposite is true.

It supports every format instantly. Because the client has no rules engine, it has no restrictions. Commander, Pauper, cubes, homebrew formats, unreleased spoiler cards, and formats nobody has invented yet all work identically, because the client is not trying to understand any of them.

It handles cards no engine supports. Cards with complicated or ambiguous text, cards from Un-sets, and anything requiring a judgment call all work, because the players make the call.

Setup takes seconds. Want to test a specific board state on turn twelve? Put the cards where they go and start playing. An enforcing client cannot do this without an elaborate setup process.

Nothing costs anything. Every card is available immediately. Testing a thousand dollar Modern deck costs nothing, which is the single most common reason people install it.

For playtesting, those four properties are worth more than automation. You are not trying to have the software referee a competitive match, you are trying to find out whether your deck works.

Where it fails

Being honest about this matters, because the failure cases are real.

It teaches the rules wrong. A player who does not know the rules will make illegal plays and nothing will correct them. Over months, that builds confidently wrong habits, and those habits transfer badly to paper events with judges.

It is slow. Every trigger, every state check, every priority pass is manual. A game that takes ten minutes on an enforcing client takes twenty-five here.

Missed triggers are common and hard to unwind. In an enforcing client the trigger happens. Here someone has to remember, and if nobody does until three turns later, the game state is a negotiation.

Disputes have no referee. When two people disagree about how an interaction works, there is nothing to appeal to except the rules text and goodwill.

Cockatrice against the alternatives

The mapping is clean once you state it plainly:

• Learning the rules: Arena, because enforcement is the teaching mechanism
• Testing a deck before buying: Cockatrice, because cards are free
• Competitive digital play: Magic Online, because it is sanctioned and enforces rules
• Playing with friends across formats: Cockatrice, because it supports everything

Table etiquette when nothing is enforced

Because the software referees nothing, the players referee each other, and games work or fall apart on a handful of shared conventions. These are worth stating because nobody tells new users and everyone assumes they are obvious.

Narrate every non-obvious action. Say what you are doing and why before you do it. “Attacking with both, the 2/2 has haste from the enchantment” prevents an argument three turns later.

Ask before you undo. Taking back a play is often reasonable, especially a misclick. Taking it back unilaterally after seeing new information is not. Ask, and accept no.

Let missed triggers go. If you forgot your own trigger and the turn has moved on, the convention in casual play is that it is missed. Rewinding three turns of a manual game to insert a trigger costs more than the trigger was worth.

Point out your opponent’s triggers. Especially ones that benefit them. This feels counterintuitive and it is what makes the format work. A table where everyone hides missed triggers is a table playing a memory game rather than Magic.

Agree the format and the rules variant up front. Since the client enforces nothing, it also verifies nothing. Whether you are playing Commander with forty life, whether a particular card is banned in your group, and whether mulligans use the London rule are all conversations, not settings.

Concede clearly. With no game state validation, an ambiguous exit leaves the other player uncertain whether you crashed or quit.

The overall principle: the software gives you total freedom, which means every bit of structure has to come from the people. Groups that establish these conventions early have good games on Cockatrice for years. Groups that do not tend to stop using it after a few frustrating sessions, and usually blame the software.

Using it well

If you are going to test on Cockatrice, a few habits make the games far more useful.

Announce triggers out loud. Type them in chat. Since nothing is automated, the chat log is the only record of what was supposed to happen, and it resolves disputes later.

Play at full speed anyway. The temptation is to take back plays, since you can. Do not. If the point is to learn whether your deck works, undoing your mistakes gives you data about a deck piloted perfectly, which is not the deck you will actually play.

Test the boring hands. The value of free testing is volume. Play the mediocre openings rather than restarting until you get a good one, because those are the hands that tell you whether your land count and curve are right.

Keep notes. Which cards were dead, which matchups were unwinnable, how often you were mana screwed. That is the entire output of a testing session, and it is easy to leave with a vague impression instead of a list.

Getting a deck into it

The mechanics of moving a decklist into the client are simple once you know the format it expects, and this is where most new users stall.

Cockatrice reads plain text decklists in the standard format used across nearly every Magic site: a quantity, a space, and the exact card name, one per line, with the sideboard separated.

4 Lightning Bolt
4 Monastery Swiftspear
20 Mountain

SB: 3 Smash to Smithereens

That means any deckbuilder that exports plain text works. Copy the list, paste it into a new deck in the client, and it resolves the names against your card database.

Two things that go wrong:

Name mismatches. If a card name does not match your database exactly, including punctuation and the double-faced card naming convention, it will not load. Cards with two faces and cards with accented characters are the usual culprits.

An outdated card database. New sets do not appear until your card data is updated. If a recent card refuses to load, that is almost always the cause rather than a typo.

For Commander specifically, the client handles the command zone through a designated zone you place the commander into manually, in keeping with the rest of its design philosophy: it gives you the zone and trusts you to use it correctly.

Who this is actually for

Worth being direct, because the answer is narrower than the enthusiasm around free Magic suggests.

Good fit: experienced players testing a deck before buying it, playgroups spread across different cities who want to play Commander together, cube designers testing a list, anyone building for an expensive eternal format.

Bad fit: brand new players, anyone wanting competitive ranked play, anyone who wants the software to handle the rules so they can focus on decisions, and anyone hoping for a permanent free replacement for a collection.

The clearest way to think about it: Cockatrice is a whiteboard, not a video game. It gives you a shared space and total freedom and no help at all. If that is what you need, nothing else does it as well. If you wanted a game that plays with you, install Arena instead.

The legality question, answered plainly

The client itself is open source software that ships with no card data. It cannot play Magic out of the box. Users supply their own card database and images separately, and that step is where the intellectual property question genuinely sits rather than in the software.

Wizards of the Coast does not endorse it. It is not a sanctioned platform, it has no official support, and no result achieved on it counts for anything.

The widely observed norm in the community is that it is used for playtesting rather than as a substitute for owning cards, in the same spirit as proxying a deck to test before buying. Whether that norm is a legal defence is not something this page will pretend to answer.

If you want to play Magic digitally with full official sanction, Arena and Magic Online are the answer. If you want to find out in an evening whether a three hundred dollar deck is worth building, this is the tool that exists.

One closing note on expectations. Because the client is community maintained and open source, its pace of change is unpredictable. Card data updates arrive when volunteers produce them, servers come and go, and the interface has not fundamentally changed in years. Treat it as a stable, unglamorous utility rather than a product with a roadmap, and it will serve you well for a long time.