Protocol

Stagehand uses bidirectional JSON-RPC. “Client” and “server” identify the sender of a message:

Term	Direction	Response expected
Client request	client → server	yes
Server request	server → client	yes
Client notification	client → server	no
Server notification	server → client	no

StagehandMethods contains request/response method contracts, regardless of which side initiates them. StagehandNotifications contains one-way notification contracts. A JSON-RPC notification is a request object without an id, so it does not receive a response.

How it works

1. schemas.ts defines protocol data with Zod.
2. schema-registry.ts assigns those schemas to JSON-RPC methods and notifications.
3. json-rpc/build-json-rpc-schema.ts derives one in-memory Zod document from those catalogs, converts it to JSON Schema, renames API-facing keys to their wire names, and writes stagehand.v4.json.
4. TypeScript uses the original Zod schemas directly. just generate uses stagehand.v4.json to generate the Python models and Go structs.

Where schemas go

• Does it cross the JSON-RPC boundary?
  • Put it in schemas.ts and infer its type with z.infer in types.ts.
  • The Zod schema is the source of truth.
• Is it used only by the SDKs?
  • Put it in ../sdk-ts/src/clientSchemas.ts, ../sdk-python/src/stagehand/client_types.py and client_models.py, and ../sdk-go/client_options.go.
  • Extend or reuse the protocol type when possible.

Adding or changing a method

1. Decide which fields cross JSON-RPC and which are used only by the SDKs.
2. Add or update the Zod schemas in schemas.ts, export their types with z.infer from types.ts, and add the method to StagehandMethods in schema-registry.ts.
3. Run just generate.
4. Implement and route the method in the extension.
   • Add it to the appropriate controller in ../extension/controllers, creating a controller if needed.
   • Put the underlying behavior in the appropriate service in ../extension/services, then route the method in ../extension/rpcRouter.ts.
5. Add or update the method in all three SDKs.
   • TypeScript: update the appropriate class in ../sdk-ts/src.
   • Python: update the corresponding class in ../sdk-python/src/stagehand.
   • Go: update the corresponding type in ../sdk-go.
6. Update the matching ../docs/v4/reference/<object>.mdx page and any affected guide.
7. Add focused tests, then run just check and just test.

Runtime protocol versions

SDK, extension, and protocol packages are versioned independently. Their package versions identify the released artifacts; only protocolVersion, sourced from this package's package.json, gates runtime compatibility.

Use standard SemVer for the protocol:

Bump	Use when
Patch	Correcting the protocol without requiring a new runtime capability
Minor	Adding a backward-compatible capability that a newer client may require
Major	Breaking communication with a previously released client or server, including transport changes

Do not bump the protocol for an SDK-only or extension-only implementation change. A breaking public SDK API with no wire change affects that SDK's package version, not the protocol version.

Stable releases are compatible when the client and server protocol majors match and the server protocol minor is greater than or equal to the client protocol minor. Protocol patch differences are compatible. Prerelease protocol versions must match exactly.

In short: if a new client must reject an older extension, bump the protocol minor; if an existing released client or server can no longer communicate correctly, bump the protocol major.

Keep RuntimeDescriptorSchema TypeScript-only. The runtime marker is read as a camel-cased JavaScript object through CDP, not through the snake-cased JSON-RPC schema artifact.