frontmcp-extensibility

Use when extending FrontMCP beyond the core SDK by integrating external npm packages, libraries, or third-party services into providers and tools. Covers VectoriaDB for in-memory semantic and vector search (ML-based embeddings or TF-IDF keyword engines, with persistence) and the tamper-evident, hash-chained skill audit log (pluggable signer and store, with chain verification). Triggers: add semantic search, vector search, embeddings, similarity search, recommendations, ML features, audit logging, or integrate an external library, database, or API beyond the built-in SDK.

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name	frontmcp-extensibility
description	Use when extending FrontMCP beyond the core SDK by integrating external npm packages, libraries, or third-party services into providers and tools. Covers VectoriaDB for in-memory semantic and vector search (ML-based embeddings or TF-IDF keyword engines, with persistence) and the tamper-evident, hash-chained skill audit log (pluggable signer and store, with chain verification). Triggers: add semantic search, vector search, embeddings, similarity search, recommendations, ML features, audit logging, or integrate an external library, database, or API beyond the built-in SDK.
tags	["extensibility","vectoriadb","search","integration","npm","provider","external-services"]
category	extensibility
targets	["all"]
bundle	["full"]
priority	10
visibility	both
license	Apache-2.0
metadata	{"docs":"https://docs.agentfront.dev/frontmcp/extensibility/providers"}

FrontMCP Extensibility

Patterns and examples for extending FrontMCP servers with external npm packages. The core SDK handles MCP protocol, DI, and lifecycle — this skill shows how to integrate third-party libraries as providers and tools.

When to Use This Skill

Must Use

Adding semantic search or similarity matching to your server (VectoriaDB)
Integrating an external npm package as a FrontMCP provider
Building tools that wrap third-party services (databases, APIs, ML models)

Recommended

Looking for patterns to structure external service integrations
Deciding between provider-based vs direct integration for a library
Adding capabilities like applescript automation, VM execution, or data processing

Skip When

You need to build core MCP components (see frontmcp-development)
You need to configure auth, transport, or CORS (see frontmcp-config)
You need to write a plugin with hooks and context extensions (see create-plugin)

Decision: Use this skill when integrating external libraries into your FrontMCP server as providers or tools.

Prerequisites

A FrontMCP project (see frontmcp-setup if you don't have one).
The external library installed as a runtime dependency (not devDependency).
Familiarity with FrontMCP providers and tools (see create-provider, create-tool).

Steps

Pick the integration shape — provider for stateful clients (DB, search index), tool-only for stateless one-shot calls.
Wrap the library in a provider — declare a typed DI token and a @Provider class so consumers depend on the boundary, not the library.
Register it — add to @App({ providers: [...] }) or @FrontMcp({ providers: [...] }).
Expose via tools/resources — call this.get(TOKEN) in ToolContext/ResourceContext; never import the library directly from the tool.
Handle errors at the boundary — translate library-specific errors into PublicMcpError/InvalidInputError so MCP clients see structured failures.

Scenario	Reference	Description
Add in-memory semantic search with VectoriaDB	`references/vectoriadb.md`	TF-IDF or ML semantic indexing, provider+tool pattern
Add tamper-evident skill audit logging	`references/skill-audit-log.md`	Hash-chained, signed audit records for skill executions
Load an app from an npm package	`multi-app-composition` (in frontmcp-setup)	`App.esm('@scope/pkg@^1.0.0', 'AppName')` pattern
Connect to a remote MCP server	`multi-app-composition` (in frontmcp-setup)	`App.remote('https://...', 'ns')` pattern
Build a reusable plugin with hooks	`create-plugin-hooks` (in frontmcp-development)	`DynamicPlugin`, context extensions, lifecycle hooks
Build a custom adapter for an external source	`create-adapter` (in frontmcp-development)	`DynamicAdapter` for OpenAPI, GraphQL, or custom sources
Auto-generate tools from an OpenAPI spec	`official-adapters` (in frontmcp-development)	`OpenapiAdapter` with filtering, auth, and transforms

// 1. Provider wraps the library (the class itself is the DI token)
@Provider({ name: 'my-search', scope: ProviderScope.GLOBAL })
export class SearchProvider {
  private client: ExternalLibrary;
  constructor() {
    this.client = new ExternalLibrary({
      /* config */
    });
  }
  async search(query: string) {
    return this.client.query(query);
  }
}

// 2. Tool exposes it
@Tool({ name: 'search', inputSchema: { query: z.string() } })
export default class SearchTool extends ToolContext {
  async execute(input: { query: string }) {
    return this.get(SearchProvider).search(input.query);
  }
}

Pattern	Correct	Incorrect	Why
Library access	`this.get(SearchToken)` from a tool	`import { client } from 'lib'` in a tool	DI boundary lets you swap implementations and test in isolation
Provider scope	`ProviderScope.GLOBAL` for shared clients	New instance per request	Library clients (DB pools, indices) are expensive to construct
Async initialisation	`onInit()` lifecycle hook on the provider	Constructor `await`	Constructors can't be async; `onInit` is the framework's init seam
Error surfaces	Throw `PublicMcpError`/`InvalidInputError`	Re-throw raw library errors	Library stack traces leak internals and aren't JSON-RPC error-coded

Problem	Cause	Solution
`Cannot find module '<lib>'` at runtime	Library declared as `devDependency` only	Move to `dependencies`; rebuild the bundle if deploying as MCPB/CLI
Provider constructed once per request	Default scope used; expensive client recreated each call	Set `scope: ProviderScope.GLOBAL` on the `@Provider` decorator
Tool sees `undefined` from `this.get(TOKEN)`	Provider not registered in the active `@App`/`@FrontMcp` scope	Add the provider class to the scope's `providers: [...]` array
Browser build fails with Node-only library	Library uses `node:` modules not available at the target	Gate behind `availableWhen.platform`, or move the integration into a server-only app and call it via a remote transport

Example	Level	Description
`product-catalog-search`	Advanced	Shows advanced VectoriaDB usage with typed document metadata, batch operations, filtered search by multiple criteria, and batch indexing of a product catalog.
`semantic-search-with-persistence`	Intermediate	Shows how to use `VectoriaDB` for semantic search with transformer models, filtered search, and `FileStorageAdapter` for persistence across restarts.
`tfidf-keyword-search`	Basic	Shows how to use `TFIDFVectoria` for zero-dependency keyword search in a FrontMCP provider, with field weights and index building.

Mode	How it works
Filesystem	Read `libs/skills/catalog/frontmcp-extensibility/` directly from a clone of the catalog repo, or from a published `@frontmcp/skills` install. SKILL.md is the entry point.
`frontmcp` CLI	`frontmcp skills list`, `frontmcp skills read frontmcp-extensibility`, `frontmcp skills read frontmcp-extensibility:references/<file>.md`, `frontmcp skills install frontmcp-extensibility` — no server required.
MCP `skill://`	When a developer mounts this skill into their own FrontMCP server (`@FrontMcp({ skills: [...] })`), the SDK exposes it via SEP-2640 resources: `skill://frontmcp-extensibility/SKILL.md`, `skill://frontmcp-extensibility/references/{file}.md`, etc. The server’s `skill://index.json` returns the SEP-2640 discovery document for everything mounted on it.