feat!: Add Multichain API support #3759

FrederikBolding · 2025-12-01T11:34:17Z

Adds support for using the multichain API in Snaps. This is accomplished by setting up a separate provider and substream called metamask-multichain-provider. When snap.request is called with a multichain request, this provider and substream is used. The clients will need to route to the proper JSON-RPC pipeline based on the substream and verify that the Snap has the proper permission.

Additionally this PR adds a example Snap for usage of this API, that can leverage Ethereum and Solana APIs at once. It also adds limited simulation support for the multichain API. The simulation framework implements a basic version of the multichain API where sessions are tracked and requests are routed to supported EVM providers. There are no underlying providers for non-EVM request, but they can be mocked.

Breaking: This PR changes the default accounts used in snaps-jest to match the accounts derived from the default SRP.

Note: TBD if we hold off merging this until some bugs are squashed on extension that prevent non-EVM multichain API requests

Note

Adds first-class Multichain API support across runtime, RPC, SDK, simulation, and examples.

Execution environments: Route snap.request multichain calls via new metamask-multichain-provider substream; add isMultichainRequest and stream wiring in BaseSnapExecutor.
Permissions & endowments: Add endowment:multichain-provider and register builder; expose in permissions listing/tests.
SDK types: Add wallet_createSession, wallet_getSession, wallet_invokeMethod, wallet_revokeSession request/response types.
Simulation: New multichain middleware with session handling (create/get/revoke) and scoped wallet_invokeMethod routing; provider now respects CAIP-2 scope (EVM) and ignores non‑EVM; integrates CAIP‑25 caveat validation and simulated accounts; updates tests and defaults.
Examples & test app: New @metamask/multichain-provider-example-snap (EVM + Solana) with E2E tests; added UI in test-snaps to create/revoke sessions, switch chains, and sign.
Breaking: Default accounts updated to match default SRP (affects snaps-jest expectations).
Minor: coverage thresholds adjusted; yarn dependencies updated.

^{Written by Cursor Bugbot for commit 17795ea. This will update automatically on new commits. Configure here.}

socket-security · 2025-12-01T11:37:18Z

Review the following changes in direct dependencies. Learn more about Socket for GitHub.

Diff	Package	Supply Chain Security	Vulnerability	Quality	Maintenance	License
	@metamask/chain-agnostic-permission@1.4.0

View full report

packages/snaps-simulation/src/methods/specifications.test.ts

packages/snaps-simulation/src/methods/specifications.ts

packages/snaps-simulation/src/middleware/internal-methods/chain-id.ts

packages/snaps-simulation/src/middleware/multichain/create-session.ts

packages/snaps-simulation/src/middleware/multichain/invoke-method.ts

packages/snaps-simulation/src/middleware/multichain/utils.ts

packages/snaps-simulation/src/controllers.ts

packages/examples/packages/multichain-provider/src/modules/base.ts

codecov · 2026-01-13T14:27:08Z

Codecov Report

❌ Patch coverage is 98.93617% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 98.34%. Comparing base (b522af5) to head (17795ea).

Files with missing lines	Patch %	Lines
...s/snaps-execution-environments/src/common/utils.ts	33.33%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##             main    #3759    +/-   ##
========================================
  Coverage   98.33%   98.34%            
========================================
  Files         422      430     +8     
  Lines       12082    12250   +168     
  Branches     1876     1904    +28     
========================================
+ Hits        11881    12047   +166     
- Misses        201      203     +2

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packages/examples/packages/multichain-provider/src/modules/base.ts

packages/examples/packages/multichain-provider/src/modules/evm.ts

packages/examples/packages/multichain-provider/src/modules/sol.ts

packages/examples/packages/multichain-provider/src/index.test.ts

packages/snaps-sdk/src/types/methods/multichain/create-session.ts

packages/snaps-sdk/src/types/methods/multichain/revoke-session.ts

packages/snaps-simulation/src/middleware/multichain/middleware.ts

packages/snaps-simulation/src/controllers.test.ts

packages/snaps-simulation/src/simulation.ts

packages/examples/packages/multichain-provider/src/modules/base.ts

packages/examples/packages/multichain-provider/src/modules/sol.ts

FrederikBolding · 2026-01-16T13:23:04Z

packages/snaps-simulation/src/constants.ts

 export const DEFAULT_ACCOUNTS: SimulationAccount[] = [
  {
-    address: '0x1234567890abcdef1234567890abcdef12345678',
+    address: '0xc6d5a3c98ec9073b54fa0969957bd582e8d874bf',


I guess this may be breaking, but it makes a lot more sense for this to return the address of the default account in the simulation IMO

Yeah, this should be considered breaking.

Added note to the description

cursor

Cursor Bugbot has reviewed your changes and found 1 potential issue.

packages/examples/packages/multichain-provider/src/modules/evm.ts

cursor

Cursor Bugbot has reviewed your changes and found 1 potential issue.

packages/snaps-simulation/src/middleware/multichain/get-session.ts

cursor

Cursor Bugbot has reviewed your changes and found 1 potential issue.

packages/examples/packages/multichain-provider/src/index.ts

cursor

Cursor Bugbot has reviewed your changes and found 2 potential issues.

cursor · 2026-01-19T11:34:18Z

packages/examples/packages/multichain-provider/src/index.ts

+    case 'signTypedData': {
+      const params = request.params as SignTypedDataParams;
+      const accounts = await getAccounts(scope);
+      return await scopeModule.signTypedData(accounts[0], params.message);


Undefined account passed when accounts array is empty

Low Severity

The signMessage and signTypedData handlers use accounts[0] without checking if the array from getAccounts(scope) is empty. Since getAccounts returns session.sessionScopes[scope]?.accounts ?? [] (an empty array when no accounts exist), accounts[0] will be undefined when no session exists or the scope has no accounts. This undefined value gets passed to parseCaipAccountId() in the module methods, which will throw a confusing parsing error rather than a clear "no accounts available" message.

cursor · 2026-01-19T11:34:18Z

packages/examples/packages/multichain-provider/src/index.ts

+    case 'signTypedData': {
+      const params = request.params as SignTypedDataParams;
+      const accounts = await getAccounts(scope);
+      return await scopeModule.signTypedData(accounts[0], params.message);


Missing params validation causes crash on undefined access

Low Severity

The signMessage and signTypedData handlers cast request.params to SignMessageParams/SignTypedDataParams without validating that params exists. If a caller invokes these methods without providing params (valid in JSON-RPC), params will be undefined and accessing params.message will throw a TypeError: Cannot read properties of undefined. This is distinct from the previously reported empty accounts issue—here the crash occurs when no request params are provided at all.

FrederikBolding force-pushed the fb/multichain-api branch 2 times, most recently from 917fc58 to 491f06d Compare January 7, 2026 10:58

Mrtenz reviewed Jan 9, 2026

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FrederikBolding changed the title ~~wip: Add Multichain API support~~ feat: Add Multichain API support Jan 12, 2026

FrederikBolding force-pushed the fb/multichain-api branch from ef6f3be to 559f0ff Compare January 13, 2026 14:19

FrederikBolding requested a review from Mrtenz January 13, 2026 14:20

Mrtenz requested changes Jan 14, 2026

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FrederikBolding requested a review from Mrtenz January 14, 2026 11:08

Mrtenz requested changes Jan 15, 2026

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packages/examples/packages/multichain-provider/src/modules/base.ts Show resolved Hide resolved

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FrederikBolding commented Jan 16, 2026

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FrederikBolding added 18 commits January 16, 2026 14:25

wip: Add Multichain API support

89032df

Add example Snap

337af3c

Support signing messages with Solana

c769623

Restructure example

f77100e

Add permission boilerplate

06b724f

Add execution env test

79cf399

Update snapshots

d142d5b

Fix lint

52a4b1e

wip: Partial simulation support

dac06a5

Tweak version

40e2559

Fix lint

0f84c1e

Add genesis hash method

8ae0dee

Support creating and using multichain API sessions

19ba04b

Sync versions

0c6e0f6

Fix some more tests

a6e1563

Move multichain methods to multichain middleware

6a0aaa1

Inject accounts into session

56baddb

Fix import

5d50100

FrederikBolding added 16 commits January 16, 2026 14:26

Simplify example

4217c49

Add ScopedJsonRpcRequest type

2ced6a4

Add more tests

6d95882

Add more tests

bd63387

More tests

e14c4c5

Add wallet_revokeSession simulation

e7c7def

Add struct for wallet_invokeMethod

a13c29d

Add struct for wallet_createSession

a56c9bd

Add remaining tests

1c7044a

Resolve a bunch of comments

a73f284

Update README

ec08e8c

More JSDocs

bab46e4

Change account injection approach

792fbcf

Add tests

17f514f

Address PR comments

4ad67ba

Revert getAccountsHandler changes

a35de5f

FrederikBolding force-pushed the fb/multichain-api branch from afdf778 to a35de5f Compare January 16, 2026 13:26

FrederikBolding marked this pull request as ready for review January 16, 2026 14:52

FrederikBolding requested a review from a team as a code owner January 16, 2026 14:52

cursor bot reviewed Jan 16, 2026

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packages/examples/packages/multichain-provider/src/modules/evm.ts Outdated Show resolved Hide resolved

Fix PR comment

81c22e6

cursor bot reviewed Jan 16, 2026

View reviewed changes

packages/snaps-simulation/src/middleware/multichain/get-session.ts Show resolved Hide resolved

FrederikBolding added 2 commits January 16, 2026 16:17

Fix a type

8f299d3

Improve tests

1c442c6

FrederikBolding changed the title ~~feat: Add Multichain API support~~ feat!: Add Multichain API support Jan 19, 2026

FrederikBolding added 2 commits January 19, 2026 11:58

Adjust default Solana accounts

4cbade7

Fix assertion

2d73357

cursor bot reviewed Jan 19, 2026

View reviewed changes

packages/examples/packages/multichain-provider/src/index.ts Show resolved Hide resolved

Throw if getChainId is called for non-EVM scopes

17795ea

cursor bot reviewed Jan 19, 2026

View reviewed changes

feat!: Add Multichain API support #3759

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Undefined account passed when accounts array is empty

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Missing params validation causes crash on undefined access

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FrederikBolding commented Dec 1, 2025 •

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