Swamp Extension Model

Create TypeScript models in extensions/models/*.ts that swamp loads at startup.

When to Create a Custom Model

Create an extension model when no built-in type exists for your use case.

If you search for a type with swamp model type search <query> and get no results, you should create a custom model rather than assuming the functionality doesn't exist. Extension models let you:

• •Integrate with any API or service (AWS S3, Stripe, custom APIs, etc.)
• •Define any automation logic you need
• •Create reusable components for your workflows

Example decision flow:

1. User wants to work with S3 buckets
2. Run: swamp model type search S3 → no results
3. Solution: Create extensions/models/s3_bucket.ts with the S3 logic you need

Important: Do not default to generic CLI types (like command/shell) for specific service integrations. If the user wants to manage S3 buckets, EC2 instances, or other resources, create a dedicated model for that service rather than wrapping CLI commands.

Quick Reference

Quick Start

// extensions/models/my_model.ts
import { z } from "npm:zod@4";

const GlobalArgsSchema = z.object({ message: z.string() });

const OutputSchema = z.object({
  message: z.string(),
  timestamp: z.string(),
});

export const model = {
  type: "@myorg/my-model",
  version: "2026.02.09.1",
  globalArguments: GlobalArgsSchema,
  resources: {
    "result": {
      description: "Model output data",
      schema: OutputSchema,
      lifetime: "infinite",
      garbageCollection: 10,
    },
  },
  methods: {
    run: {
      description: "Process the input message",
      arguments: z.object({}),
      execute: async (args, context) => {
        const handle = await context.writeResource("result", "main", {
          message: context.globalArgs.message.toUpperCase(),
          timestamp: new Date().toISOString(),
        });
        return { dataHandles: [handle] };
      },
    },
  },
};

Model Structure

Resources & Files

Models declare their data outputs using resources and/or files.

Resource Specs

Resources are structured JSON data validated against a Zod schema:

resources: {
  "state": {
    description: "Deployment state",
    schema: z.object({
      status: z.string(),
      endpoint: z.string().url(),
    }),
    lifetime: "infinite",
    garbageCollection: 10,
  },
},

Spec naming: Resource spec keys must not contain hyphens (-). Use camelCase or single words (e.g., igw not internet-gateway).

Schema requirement: If your resource will be referenced by other models via CEL expressions, declare the referenced properties explicitly in the Zod schema:

// Wrong — expression validator can't resolve attributes.VpcId
schema: z.object({}).passthrough(),

// Correct — VpcId is declared so expressions can reference it
schema: z.object({ VpcId: z.string() }).passthrough(),

File Specs

Files are binary or text content (including logs):

files: {
  "log": {
    description: "Execution log",
    contentType: "text/plain",
    lifetime: "7d",
    garbageCollection: 5,
    streaming: true,
  },
},

Execute Function

The execute function receives pre-validated args and a context object:

execute: (async (args, context) => {
  // args                   - Pre-validated method arguments
  // context.globalArgs     - Global arguments
  // context.definition     - { id, name, version, tags }
  // context.methodName     - Name of the executing method
  // context.repoDir        - Repository root path
  // context.logger         - LogTape Logger
  // context.dataRepository - For advanced data operations
  // context.writeResource  - Write structured JSON data
  // context.createFileWriter - Create a writer for files

  const handle = await context.writeResource("result", "main", {
    value: "processed",
    timestamp: new Date().toISOString(),
  });

  return { dataHandles: [handle] };
});

For detailed API documentation on writeResource, createFileWriter, DataWriter, DataHandle, and dataRepository, see references/api.md.

Instance Names

The instanceName parameter on writeResource and createFileWriter sets the identifier used in CEL expressions:

writeResource("state", "current", data)
  → model.<name>.resource.state.current.attributes.<field>
                          ─────  ───────
                        specName instanceName

Convention: For single-instance resources (most models), use a descriptive instance name like main, current, or primary.

Factory models use distinct instance names to produce multiple outputs from one spec — see Factory Models below.

Factory Models

A single method execution can produce multiple dynamically-named resources from the same output spec. This is useful when a model discovers N items and needs to emit each as a separately-addressable resource.

const handles = [];
for (const subnet of subnets) {
  const handle = await context.writeResource(
    "subnet",
    subnet.subnetId, // Dynamic instance name
    subnet,
  );
  handles.push(handle);
}
return { dataHandles: handles };

Discovering factory outputs in CEL:

# Get all subnets produced by the scanner
allSubnets: ${{ data.findBySpec("my-scanner", "subnet") }}

# Access a specific named instance
subnetA: ${{ model.my-scanner.resource.subnet.subnet-aaa.attributes.cidr }}

See references/scenarios.md for complete factory model examples.

CRUD Lifecycle Models

Models that manage real resources typically have create, update, and delete methods:

• •create — run a command/API call, store the result via writeResource()
• •update — read stored data via context.dataRepository.getContent(), modify the resource, write updated state
• •delete — read stored data, clean up the resource, return { dataHandles: [] }

See references/examples.md for a complete VPC example with all three methods.

Extending Existing Model Types

Add new methods to existing model types without changing their schema. Use export const extension instead of export const model:

// extensions/models/shell_audit.ts
export const extension = {
  type: "command/shell", // target type to extend
  methods: [{
    audit: {
      description: "Audit the shell command execution",
      arguments: z.object({}),
      execute: async (args, context) => {
        const handle = await context.writeResource("result", "result", {
          exitCode: 0,
          command: `audit: ${context.definition.name}`,
          executedAt: new Date().toISOString(),
        });
        return { dataHandles: [handle] };
      },
    },
  }],
};

Extension rules:

• •Extensions cannot change the target model's Zod schema
• •Extensions only add new methods — no overriding existing methods
• •methods is always an array of Record<string, MethodDef> objects

Model Discovery

Swamp discovers models and extensions recursively:

1. •Repository extensions: {repo}/extensions/models/**/*.ts
2. •Built-in models: Bundled with swamp binary

Files are classified by export name: export const model defines new types, export const extension adds methods to existing types.

Key Rules

1. •Export: Use export const model = { ... } for new types or export const extension = { ... } for extending existing types
2. •Import: Only import { z } from "npm:zod@4"; is needed
3. •Type naming: Use @<namespace>/<name> format (e.g., @user/my-model)
4. •No type annotations: Avoid TypeScript types in execute parameters
5. •File naming: Use snake_case (my_model.ts)

Namespace Rules

User-defined models can use any namespace except reserved ones (swamp, si):

Verify

After creating your model:

swamp model type search --json              # Model should appear
swamp model type describe @myorg/my-model   # Check schema

When to Use Other Skills

References

• •API Reference: See references/api.md for detailed writeResource, createFileWriter, DataWriter, and logging API docs
• •Examples: See references/examples.md for complete model examples (CRUD lifecycle, data chaining, extensions, etc.)
• •Scenarios: See references/scenarios.md for end-to-end scenarios (custom API, cloud CRUD, factory models)
• •Troubleshooting: See references/troubleshooting.md for common errors and fixes
• •Built-in example: See src/domain/models/echo/echo_model.ts for reference
• •Model design: See design/models.md for concepts