Create Your Own Transformer

Build custom transformers for validation, enrichment, or redaction.

The transformer interface

Transformers are functions that receive a context object and return a transformer instance:

The context contains:

The returned instance must implement:

Return values

Return	Behavior
`{ event }`	Continue chain with modified event
`void`	Continue chain, event unchanged
`false`	Stop chain, event dropped
`{ event, next }`	Redirect to a different chain (fan-out)
`{ event, respond }`	Continue chain with wrapped respond function

Minimal example

Push context

The push function receives an event and a push context:

config: Transformer configuration
env: Environment dependencies
logger: Scoped logger for output
id: Transformer identifier
collector: Access to collector instance
ingest: Request metadata from source (optional)

Examples

Enrich: add server-side data

Validate: custom check

Using your transformer

Testing

Package convention

Every walkerOS package includes machine-readable metadata for tooling and discovery.

`walkerOS` field in package.json

Field	Required	Description
`walkerOS`	Yes	Object with `type` metadata (and `platform` for sources/destinations)

Build-time generation

Use buildDev() from the shared tsup config to auto-generate walkerOS.json:

This file contains your package's JSON Schemas and examples, enabling MCP tools and the CLI to validate configurations without installing your package.

Optional: Hints

Packages can export a hints record from src/dev.ts to provide lightweight, actionable context beyond schemas and examples, such as validation behavior, enrichment patterns, or troubleshooting tips. Hints are serialized into walkerOS.json and surfaced via MCP tools. See the walkeros-create-transformer skill for details.

Publishing checklist

walkerOS field in package.json
Keywords include walkeros and walkeros-transformer
buildDev() in tsup.config.ts
dist/walkerOS.json generated on build
npm run test passes
npm run lint passes

Next steps

Review Validator source as reference
Learn about creating sources
Learn about creating destinations

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The transformer interface​

Return values​

Minimal example​

Push context​

Examples​

Enrich: add server-side data​

Validate: custom check​

Using your transformer​

Testing​

Package convention​

walkerOS field in package.json​

Build-time generation​

Optional: Hints​

Publishing checklist​

Next steps​