Agent Kit Plugin

Creating Hedera Agent Kit Plugins

This skill provides guidance for creating custom plugins that extend the Hedera Agent Kit. Plugins allow adding new tools for Hedera network interactions—token operations, account management, consensus service, smart contracts, and custom integrations.

Quick Start

To create a Hedera plugin in 5 steps:

1. Install dependencies: Set up a TypeScript project with @hashgraph/hedera-agent-kit and @hiero-ledger/sdk
2. Create plugin structure: Create an index.ts with the plugin definition and a tools/ directory
3. Define tools: Each tool is a class extending BaseTool — this opts the tool into the hooks/policies lifecycle
4. Export properly: Export the plugin object and tool name constants
5. Register with agent: Import and pass the plugin in the toolkit configuration.plugins array

Plugin Interface

Every Hedera plugin implements this interface from @hashgraph/hedera-agent-kit:

import { Plugin } from '@hashgraph/hedera-agent-kit';

export interface Plugin {
  name: string;           // Unique kebab-case identifier
  version?: string;       // Semantic version (e.g., "1.0.0")
  description?: string;   // Brief explanation of plugin purpose
  tools: (context: Context) => Tool[];  // Factory returning tools
}

The tools function receives a Context object containing network configuration and returns an array of Tool objects. BaseTool itself implements Tool, so a BaseTool subclass instance is a valid return value.

BaseTool

Tools are written as classes extending BaseTool, which implements Tool and runs a 7-stage lifecycle:

[1] preToolExecutionHook
[2] normalizeParams        ← your logic
[3] postParamsNormalizationHook
[4] coreAction             ← your logic
[5] postCoreActionHook
[6] secondaryAction        ← your logic (skipped via shouldSecondaryAction for queries)
[7] postToolExecutionHook

Hooks and policies registered on the agent kit fire at stages 1, 3, 5, and 7 automatically — you never call them manually.

A subclass must provide:

Optional overrides: outputParser, shouldSecondaryAction (return false for query-only tools), handleError, and the four hook methods.

Tool Types

Mutation tools — state-changing operations (token create/mint/transfer, account update, topic submit). coreAction builds the Transaction, secondaryAction calls handleTransaction(). Use transactionToolOutputParser.

Query tools — read-only operations (token info, balances, mirror-node fetches). coreAction returns the result directly. Override shouldSecondaryAction to return false. Use untypedQueryOutputParser.

File Structure Pattern

Follow this structure for all Hedera plugins:

my-hedera-plugin/
├── index.ts                    # Plugin definition and exports
└── tools/
    └── category/               # Group related tools
        ├── create-something.ts
        └── get-something.ts

Creating a Tool

Step 1: Define the Tool Constant

export const MY_TOOL_NAME = 'my_tool_name_tool';

Use UPPER_SNAKE_CASE with _TOOL suffix for the constant. The value should be lowercase snake_case.

Step 2: Create the Prompt Function

const myToolPrompt = (context: Context = {}) => {
  return `This tool does X on Hedera.
Parameters:
- param1 (str, required): Description of param1
- param2 (int, optional): Description of param2, defaults to 0`;
};

Step 3: Define Parameters with Zod

import { z } from 'zod';

const myToolParameters = (_context: Context = {}) => {
  return z.object({
    param1: z.string().describe('Description of param1'),
    param2: z.number().optional().describe('Description of param2'),
  });
};

type MyToolParams = z.infer<ReturnType<typeof myToolParameters>>;

See references/zod-schema-patterns.md for common Hedera parameter patterns.

Step 4: Implement the BaseTool subclass (mutation example)

import { Client, Status } from '@hiero-ledger/sdk';
import {
  BaseTool,
  Context,
  handleTransaction,
  RawTransactionResponse,
  transactionToolOutputParser,
} from '@hashgraph/hedera-agent-kit';

const postProcess = (response: RawTransactionResponse) =>
  `Operation completed.
Transaction ID: ${response.transactionId}`;

export class MyTool extends BaseTool<MyToolParams, MyToolParams> {
  method = MY_TOOL_NAME;
  name = 'My Tool Display Name';
  description: string;
  parameters: ReturnType<typeof myToolParameters>;
  outputParser = transactionToolOutputParser;

  constructor(context: Context) {
    super();
    this.description = myToolPrompt(context);
    this.parameters = myToolParameters(context);
  }

  // Stage 2 — resolve defaults
  async normalizeParams(params: MyToolParams) {
    return params;
  }

  // Stage 4 — build the transaction (do not sign here)
  async coreAction(params: MyToolParams, _context: Context, _client: Client) {
    // return new SomeTransaction()...;
    return undefined as any;
  }

  // Stage 6 — sign and submit
  async secondaryAction(transaction: any, client: Client, context: Context) {
    return handleTransaction(transaction, client, context, postProcess);
  }

  async handleError(error: unknown) {
    const message = 'Failed to execute' + (error instanceof Error ? `: ${error.message}` : '');
    console.error(`[${MY_TOOL_NAME}]`, message);
    return { raw: { status: Status.InvalidTransaction, error: message }, humanMessage: message };
  }
}

Step 5: Export a Factory

const tool = (context: Context): BaseTool => new MyTool(context);
export default tool;

The factory pattern lets the plugin's tools(context) function instantiate a fresh tool per request with the right context bound.

Query-tool variant — skip stage 6

For read-only tools, override shouldSecondaryAction so the lifecycle stops after coreAction, and have secondaryAction pass the result through unchanged:

export class MyQueryTool extends BaseTool<MyToolParams, MyToolParams> {
  // ... method/name/description/parameters as above ...
  outputParser = untypedQueryOutputParser;

  async normalizeParams(params: MyToolParams) {
    return params;
  }

  async coreAction(params: MyToolParams, _context: Context, client: Client) {
    return await someHederaQuery(params, client);
  }

  async shouldSecondaryAction() {
    return false;
  }

  async secondaryAction(result: any) {
    return result;
  }
}

Creating the Plugin Index

import { Context, Plugin } from '@hashgraph/hedera-agent-kit';
import myTool, { MY_TOOL_NAME } from './tools/category/my-tool';

export const myPlugin: Plugin = {
  name: 'my-hedera-plugin',
  version: '1.0.0',
  description: 'A plugin for custom Hedera operations',
  tools: (context: Context) => {
    return [
      myTool(context),
    ];
  },
};

export const myPluginToolNames = {
  MY_TOOL_NAME,
} as const;

export default { myPlugin, myPluginToolNames };

Post-Processing Results

secondaryAction typically delegates to handleTransaction, which calls a postProcess function with the raw transaction response:

const postProcess = (response: RawTransactionResponse) => {
  if (response.scheduleId) {
    return `Scheduled transaction created.
Transaction ID: ${response.transactionId}
Schedule ID: ${response.scheduleId.toString()}`;
  }
  return `Operation completed.
Transaction ID: ${response.transactionId}`;
};

RETURN_BYTES mode — raw.bytes is a Uint8Array

When a tool runs in RETURN_BYTES mode, raw.bytes returned by ResponseParserService is always a plain Uint8Array in both Node.js and browser environments. Pass it directly to Transaction.fromBytes() — no manual conversion is needed.

const bytes = toolCall.parsedData.raw.bytes;
const tx = Transaction.fromBytes(bytes);

Naming Conventions

Common Imports

// From @hashgraph/hedera-agent-kit (core)
import {
  Context,
  Plugin,
  BaseTool,
  handleTransaction,
  RawTransactionResponse,
  transactionToolOutputParser,
  untypedQueryOutputParser,
} from '@hashgraph/hedera-agent-kit';

// Built-in plugins live in the /plugins subpath
import { coreTokenPlugin, coreAccountPlugin } from '@hashgraph/hedera-agent-kit/plugins';

// Hedera SDK is a peer dependency
import { Client, Status } from '@hiero-ledger/sdk';

// For parameter validation
import { z } from 'zod';

Additional Resources

Reference Files

For detailed patterns and techniques, consult:

• references/plugin-interface.md - Plugin interface, BaseTool lifecycle in depth
• references/zod-schema-patterns.md - Common Zod schemas for Hedera parameters
• references/prompt-patterns.md - Prompt generation patterns for tool descriptions
• references/error-handling.md - Error handling and output parsing patterns

Example Files

Working examples in examples/:

• examples/simple-plugin/ - Minimal BaseTool query (starter template)
• examples/token-plugin/ - Mutation (CreateTokenTool) and query (GetTokenInfoTool) BaseTool subclasses

Best Practices

1. One file per tool, named after the tool in kebab-case
2. Group related tools under category directories in tools/
3. Stable class names: <DoesWhat>Tool (e.g., CreateTokenTool)
4. Resolve defaults in normalizeParams, not in coreAction — keeps the build step pure
5. Build, don't submit, in coreAction — submission belongs in secondaryAction where hooks can react
6. Override handleError so logs are tagged with the tool method
7. Validate with Zod's .describe() — every field; descriptions guide the agent
8. Export tool name constants so consumers can reference tools programmatically

Registering a Plugin with a Toolkit

Plugins are passed explicitly to the toolkit you choose. Toolkits live in dedicated packages — pick the one that matches your framework:

Empty plugins array means zero tools. List every plugin you need explicitly, or use allCorePlugins from the /plugins subpath to load every built-in core plugin at once.

import { Client, PrivateKey } from '@hiero-ledger/sdk';
import { AgentMode } from '@hashgraph/hedera-agent-kit';
import { coreTokenPlugin, coreAccountPlugin } from '@hashgraph/hedera-agent-kit/plugins';
import { HederaLangchainToolkit } from '@hashgraph/hedera-agent-kit-langchain';
import { myPlugin } from './my-hedera-plugin';

const client = Client.forTestnet().setOperator(
  process.env.ACCOUNT_ID!,
  PrivateKey.fromStringECDSA(process.env.PRIVATE_KEY!),
);

const toolkit = new HederaLangchainToolkit({
  client,
  configuration: {
    plugins: [coreTokenPlugin, coreAccountPlugin, myPlugin],
    context: { mode: AgentMode.AUTONOMOUS },
  },
});

const tools = toolkit.getTools();

To load every built-in core plugin at once, import allCorePlugins:

import { allCorePlugins } from '@hashgraph/hedera-agent-kit/plugins';
// ...
plugins: [...allCorePlugins, myPlugin],

Workflow Summary

1. Create plugin directory with index.ts and tools/ subdirectory
2. For each tool, write a BaseTool subclass and a factory function in its own file
3. Export tools from index.ts along with tool name constants
4. Pass the plugin in the toolkit's configuration.plugins array
5. Tools become available to the AI agent

For complete working examples, see the examples/ directory.