Matrix Specification Proposals

This repository contains proposals for changes to the Matrix Protocol, aka "Matrix Spec Changes" (MSCs). The proposals directory contains MSCs which have been accepted.

See below for instructions for creating new proposals. See also https://spec.matrix.org/proposals/ for more information on the MSC process, in particular https://spec.matrix.org/proposals/#process.

The source of the Matrix specification itself is maintained at https://github.com/matrix-org/matrix-spec.

The Matrix Spec Process

An MSC is meant to be a technical document that unambiguously describes a change to the Matrix Spec, while also justifying why the change should be made.

The document is used both to judge whether the change should be made as described and by developers to actually implement the changes. This is why it's important for an MSC to be fully fleshed out in technical detail, as once merged it's immediately part of the formal spec (even though it still needs to be transcribed into the actual spec itself).

What changes need to follow this process?

In most cases a change to the Matrix protocol will require an MSC. Changes that would not require an MSC are typically small and uncontentious, or are simply clarifications to the spec. Fixing typos in the spec do not require an MSC. In most cases, removing ambiguities do not either. The exception may be if implementations in the ecosystem have differing views on clarifying the ambiguity. In that case, an MSC is typically the best place to reach consensus.

Ultimately, the Spec Core Team have the final say on this, but generally if the change would require updates to a non-insignificant portion of the Matrix implementation ecosystem or would be met with contention, an MSC is the best route to take. You can also ask in the Matrix Spec or Office of the Spec Core Team Matrix rooms for clarification.

Summary of the process

The MSC process consists of three basic steps:

1. Write up the proposal in a markdown document. (There's a proposal template, but don't feel bound by it.)
2. Submit it as a Pull Request to this repo, marking it as a draft until it's ready for wider review.
3. Seek review from the community. Once people are generally happy with it, ask the Spec Core Team to look at it in the Office of the SCT Matrix room. When the SCT are happy with the proposal, and after a successful voting process, your pull request is merged and the MSC is now officially accepted as part of the Matrix Spec and can be used 🎉

For simple changes this is really all you need to know. For larger or more controversial changes, getting an MSC merged can take more time and effort, but the overall process remains the same.

Below is various guidance to try and help make the experience smoother.

Guidance on the process

1. Writing the proposal

Come up with an idea. The idea can be for anything, but the solution (MSC) needs to benefit the Matrix ecosystem rather than yourself (or your company) specifically. Sometimes this means that the solution needs to be more generic than the specific itch that you are trying to scratch.

Remember that an MSC is a formal technical document which will be used by others in the wider community to judge if the proposal should be accepted and to actually implement the changes in clients and servers. This means that for an MSC to be accepted it should include justifications and describe the technical changes unambiguously, including specifying what happens in any and all edge cases.

There's a proposal template under docs/0000-proposal.md, but you don't necessarily need to use it. Covering the same major points is fine.

• Note: At this stage, you won't have an MSC number, so feel free to use 0000, XXXX, or whatever other placeholder you feel comfortable with.

Some tips for MSC writing:

• Please wrap your lines to 120 characters maximum. This allows readers to review your markdown without needing to horizontally scroll back and forth. Many markdown text editors have this feature.
• If you are referencing an existing endpoint in the spec, or another MSC, it is very helpful to add a link to them so the reader does not need to search themselves. Examples:
  • "This MSC proposals an alternative to MSC3030."
  • "A new field will be added to the response body of /_matrix/client/v3/sync".
    • Note: it is best to link to the latest stable version of the spec (e.g. /v1.3, not /latest) - failing that, /unstable if the change is not yet in a released spec version.
• GitHub supports rendering fancy diagrams from text with very little effort using Mermaid. See this guide for more information.
• Take a look at the MSC Checklist. When it comes time for the Spec Core Team to review your MSC for acceptance, they'll use the items on this checklist as a guide.

2. Submitting a Pull Request

1. Open a Pull Request to add your proposal document to the proposals directory. Note that this will require a GitHub account.
   • Mark your Pull Request as a draft for now.
2. The MSC number is the number of the pull request that is automatically assigned by GitHub. Go back through and edit the document accordingly. Don't forget the file name itself!
3. Edit the pull request title to fit the format "MSC1234: Your proposal title".
4. Once your proposal is correctly formatted and ready for review from the wider ecosystem, take your Pull Request out of draft status.

The Spec Core Team will notice this and apply various labels/status tracking to your MSC, which will announce it to the wider world.

3. Seeking review

Seek review from the Matrix community. Generally this will happen naturally, but if you feel that your proposal is lacking review then ask for people's opinion in the Matrix Spec room on Matrix.

Reviews can take many forms, and do not need to be done solely by members of the Spec Core Team. Getting other people who are familiar with the area of Matrix you are proposing changes to is a great first step; especially those who may be implementing these changes in clients and/or homeservers.

While the proposal is a work in progress, it's fine for it to be high level and hand-wavy in places, but remember that before it can be accepted it needs to be expanded to fully flesh out all the technical detail and edge cases.

At this stage the proposal should also be implemented as a proof of concept somewhere to show that it actually works in practice. This can be done on any client or server and doesn't need to be merged or released.

4. Entering Final Comment Period

After the MSC has been implemented, fully fleshed out, and generally feels ready for final review, you should ask a member of the Spec Core Team to review it in the public Spec Core Team Office room on Matrix. Someone from the SCT will then review it, and if all looks well will propose FCP to start.

At this point, other members of the SCT will look at the proposal and consider it for inclusion in the spec.

After enough SCT members have approved the proposal, the MSC will enter something called Final Comment Period. This is a 5 calendar day countdown to give anyone one last chance to raise any blockers or concerns about the proposed change. Typically MSCs pass this stage without incident, but it nevertheless serves as a safeguard.

5. The MSC is accepted

Once FCP has ended and the MSC pull request is merged, the proposed change is considered officially part of the spec. Congratulations!

Clients and servers can now start using the change, even though at this stage it still needs to be transcribed into the spec document. This happens over in https://github.com/matrix-org/matrix-spec/ and you are very welcome to do it yourself! Otherwise it will be handled by a Spec Core Team member. If you would like help with writing spec PRs, feel free to join and ask questions in the Matrix Spec and Docs Authoring Room on Matrix.

Other useful information

Unstable prefixes

"Unstable prefixes" are the namespaces which are used by implementations while an MSC is not yet accepted.

For instance, an MSC might propose that a m.space event type or an /_matrix/client/v1/account/whoami endpoint should exist. However, implementations cannot use these stable identifiers until the MSC has been accepted, as the underlying design may change at any time; the design is unstable.

Instead, an MSC can define a namespace such as org.matrix.msc1234 (using the real MSC number once known) which is added to the stable identifier, allowing for breaking changes between edits of the MSC itself, and preventing clashes with other MSCs that might attempt to add the same stable identifiers.

For the above examples, this would mean using org.matrix.msc1234.space and /_matrix/client/unstable/org.matrix.msc1234/account/whoami. It is also fine to use more traditional forms of namespace prefixes, such as com.example.* (e.g. com.example.space).

Note: not all MSCs need to make use of unstable prefixes. They are only needed if implementations of your MSC need to exist in the wild before your MSC is accepted, and the MSC defines new endpoints, field names, etc.

Unstable feature flags

It is common when implementing support for an MSC that a client may wish to check if the homeserver it is communicating with supports an MSC. Typically, this is handled by the MSC defining an entry in the unstable_features dictionary of the /_matrix/client/versions endpoint, in the form of a new entry:

{
  "unstable_features": {
    "org.matrix.msc1234": true
  }
}

... with a value of true indicating that the feature is supported, and false or lack of the field altogether indicating the feature is not supported.

When can I use stable identifiers?

According to the spec process: once an MSC has been accepted, implementations are allowed to switch to stable identifiers. However, the MSC is still not yet part of a released spec version.

In most cases, this is not an issue. For instance, if your MSC specifies a new event type, you can now start sending events with those types!

Some MSCs introduce functionality where coordination between implementations is needed. For instance, a client may want to know whether a homeserver supports the stable version of a new endpoint before actually attempting to request it. Or perhaps the new event type you're trying to send relies on the homeserver recognising that new event type, and doing some work when it sees it.

At this point, it may be best to wait until a new spec version is released with your changes. Homeservers that support the changes will eventually advertise that spec version under /versions, and your client can check for that.

But if you really can't wait, then there is another option: the homeserver can tell clients that it supports stable indentifiers for your MSC before it enters a spec version, using yet another unstable_features flag:

{
  "unstable_features": {
    "org.matrix.msc1234": true,
    "org.matrix.msc1234.stable": true
  }
}

If a client sees that org.matrix.msc1234.stable is true, it knows that it can start using stable identifiers for the new MSC, and the homeserver will accept and act on them accordingly.

Note: While the general pattern of using the text ".stable" has emerged from previous MSCs, you can pick any name you like. You need only to clearly state their meaning, usually under an "Unstable prefixes" header in your MSC.

See MSC3827 for a good example of an MSC that wanted to use such a flag to speed up implementation rollout, and how it did so.

Room versions

To summarize the spec on room versions: they are how servers agree upon algorithms in a decentralized world like ours. Examples of changes that require a new room version include anything that changes:

• The format of the core event structure (such as renaming a top-level field, or modifying the redaction algorithm), therefore altering the reference hash of an event.
• The authorisation of events (such as changes to power levels).

Unstable prefixes (see above) for room versions work the same as they do for other identifiers; your unstable room version may be called "org.matrix.msc1234".

In order for the changes to end up in a "real" room version (the ones listed in the spec), it will need a second MSC which aggregates a bunch of functionality from various MSCs into a single room version. Typically these sorts of curating MSCs are written by the Spec Core Team given the complexity in wording, but you're more than welcome to bring an MSC forward which makes the version real.

For an example of what introducing a new room version-required feature can look like, see MSC3667. For an example of what making a new "real" room version looks like, see MSC3604.

Ownership of MSCs and closing them

If an author decides that they would no longer like to pursue their MSC, they can either pass ownership of it off to someone else, or close it themselves.

• The author of an MSC can close their MSC at any time before FCP by simply closing the pull request.

• To appoint another user as an author of the MSC (either to replace the author entirely or to provide additional help), make a note in the MSC's PR description by writing the following on its own line:

  Author: @username
  

  where @username is a valid GitHub username. Multiple such lines can be added.

  Finally, give that user access to write to your fork of matrix-spec-proposals on GitHub, which your PR originates from. This will allow them to change the text of your MSC.

Similar to accepting an MSC, the Spec Core Team may propose a Final Comment Period with a disposition of "close". This can happen if the MSC appears abandoned by its author, or the idea is widely rejected by the community. A vote and final comment period will still be required for the motion to pass.

Additionally, FCP can be also proposed with a disposition of "postpone". This may be done for MSCs for which the proposed changes do not make sense for the current state of the ecosystem, but may make sense further down the road.

Asking for help

The Matrix community and members of the Spec Core Team are here to help guide you through the process!

If you'd just like to get initial feedback about an idea that's not fully fleshed out yet, creating an issue at https://github.com/matrix-org/matrix-spec/issues is a great place to start. Be sure to search for any existing issues first to see if someone has already had the same idea!

A few official rooms exist on Matrix where your questions can be answered, or feedback on your proposal can be requested:

• #matrix-spec:matrix.org - General chat for MSCs, the spec, and pretty much anything in that sphere.
• #sct-office:matrix.org - Where the Spec Core Team hangs out and is available. This room is intended to have extremely high signal and low noise, primarily to ensure that MSCs are not falling through the cracks. If an MSC requires attention or comment from Spec Core Team members, bring it up here.
• #matrix-spec-process:matrix.org - A room dedicated to the spec process itself. If you have any questions about or suggestions to improve the Matrix Spec process, ask them here.
• #matrix-docs:matrix.org - A quieter room for discussion of the formal spec text and matrix.org website.