Valve has updated its rules and guidelines for developers who intend to release games on Steam Early Access.

The updated rules and guidelines, first reported by GiantBomb and verified by Eurogamer, state that Early Access is "meant to be a place for games that are in a playable alpha or beta state, are worth the current value of the playable build, and the developer plans to continue to develop for release".

Early Access title DayZ has a clear warning about its current status.

It mentions the expectation among gamers that Early Access titles should be developed to a point that is considered a "finished" game.

The tightened rules come following a raft of high-profile cases in which players have complained about the poor quality of Steam Early Access games - and in some cases the lack of updates post-launch.

While Early Access, which is designed to let developers sell games before they're finished in order to gain feedback and make improvements, has seen huge successes, such as DayZ, Rust and Starbound, it's also seen its fair share of controversy.

In May Valve hauled first-person sci-fi post-apocalyptic open-world game Earth: Year 2066 from Steam Early Access and offered refunds to disgruntled customers after the game had been labelled "broken" and unfit for sale.

The developer, Killing Day Studios, had also been accused of misleading customers with inaccurate claims on the game's Steam product page.

And last month Brütal Legend and Broken Age developer Double Fine hit the headlines when it announced it had stopped work on Spacebase DF-9 because it wasn't generating enough money to justify continued investment. In the end Double Fine offered a free copy of its dungeon crawler Hack 'n' Slash to those who had bought Spacebase DF-9.

"When you launch a game in Steam Early Access, there is an expectation by customers that you will continue development to a point where you have what you consider a 'finished' game," reads Valve's new document.

"We know that nobody can predict the future, and circumstances frequently change, which may result in a game failing to reach a 'finished' state, or may fail to meet customer expectations in some other way. We work hard to make sure this risk is communicated clearly to customers, but we also ask that developers follow a set of rules that are intended to help inform customers and set proper expectations when purchasing your game."

Of the four new rules, number two is of most interest: "Do not make specific promises about future events."

"For example, there is no way you can know exactly when the game will be finished, that the game will be finished, or that planned future additions will definitely happen. Do not ask your customers to bet on the future of your game. Customers should be buying your game based on its current state, not on promises of a future that may or may not be realised."

There are four new guidelines, too. We've republished them below.

Don't launch in Early Access if you can't afford to develop with very few or no sales.

There is no guarantee that your game will sell as many units as you anticipate. If you are counting on selling a specific number of units to survive and complete your game, then you need to think carefully about what it would mean for you or your team if you don't sell that many units. Are you willing to continue developing the game without any sales? Are you willing to seek other forms of investment?

Make sure you set expectations properly everywhere you talk about your game.

For example, if you know your updates during Early Access will break save files or make the customer start over with building something, make sure you say that up front. And say this everywhere you sell your Steam keys.

Don't launch in Early Access without a playable game.

If you have a tech demo, but not much gameplay yet, then it's probably too early to launch in Early Access. If you are trying to test out a concept and haven't yet figured out what players are going to do in your game that makes it fun, then it's probably too early. You might want to start by giving out keys to select fans and getting input from a smaller and focused group of users before you post your title to Early Access. At a bare minimum, you will need a video that shows in-game gameplay of what it looks like to play the game. Even if you are asking customers for feedback on changing the gameplay, customers need something to start with in order to give informed feedback and suggestions.

Don't launch in Early Access if you are done with development.

If you have all your gameplay defined already and are just looking for final bug testing, then Early Access isn't the right place for that. You'll probably just want to send out some keys to fans or do more internal playtesting. Early Access is intended as a place where customers can have impact on the game.

Of particular interest is the first guideline: "Don't launch in Early Access if you can't afford to develop with very few or no sales." If it's followed, it should ensure situations like the one Double Fine found itself in with Spacebase DF-9.

While worded strongly, these guidelines are just that: guidelines. It remains to be seen whether developers of Early Access games will follow them.