---
title: Introduction
description: Seamline guards the seams between your services — API contracts with Specdiff and environment configuration with Envlock.
url: https://pr-1-ff84656b4b8a.thally.app/
---

# Introduction

Seamline guards the seams between your services — API contracts with Specdiff and environment configuration with Envlock.

Seamline is a TypeScript toolkit that catches contract mismatches before they reach production. It targets two seams where services break silently: **API schemas** and **environment configuration**.

**Specdiff** detects breaking changes between two versions of a JSON Schema or OpenAPI document. Point it at a before and after file, and it reports every addition, removal, and constraint change, ranked by severity (`breaking`, `warning`, `info`). Use it in pull-request checks to block incompatible API changes automatically.

**Envlock** turns environment variables into a typed, validated contract. Declare the shape of your configuration once, then verify that any `.env` file or live `process.env` satisfies it. Missing keys, wrong types, and undeclared variables surface immediately instead of at runtime.

Together the two products cover both sides of a service boundary: Specdiff guards what you **send** (API schemas), and Envlock guards what you **receive** (configuration from the deployment environment).

### Packages

Each product ships three packages:

| | Core library | CLI | MCP server |
| --- | --- | --- | --- |
| **Specdiff** | `@specdiff/core` | `@specdiff/cli` | `@specdiff/mcp` |
| **Envlock** | `@envlock/core` | `@envlock/cli` | `@envlock/mcp` |

The core library has zero runtime dependencies and works in any Node.js application. The CLI wraps the core for terminal and CI use. The MCP server exposes the same functionality to AI-powered editors and tools.

### Requirements

- **Node.js 22** or later
- **ESM only** -- all packages use `"type": "module"`
- **TypeScript** recommended (full type definitions included)

### Next steps

#### [Quickstart](/quickstart)

    Install and run both tools in under five minutes.

#### [Specdiff overview](/specdiff/overview)

    Learn how breaking-change detection works.

#### [Envlock overview](/envlock/overview)

    Define and validate your first environment contract.