---
title: Seamline
description: A toolkit for guarding API and configuration contracts so breaking changes never reach production unnoticed.
url: https://pr-1-20d929b47ede.thally.app/
---

# Seamline

A toolkit for guarding API and configuration contracts so breaking changes never reach production unnoticed.

## What is Seamline?

Seamline is a pair of lightweight, zero-config libraries that protect the seams where your services connect: the API surface and the runtime environment.

### Specdiff -- breaking-change detection

Specdiff compares two versions of a JSON Schema or OpenAPI document and reports every breaking change, warning, and informational difference it finds. A 45-rule catalogue covers endpoints, parameters, request bodies, responses, security requirements, and schema-level constraints. Run it as a library (`@specdiff/core`), a CLI (`@specdiff/cli`), or an MCP server (`@specdiff/mcp`) for AI-assisted workflows.

### Envlock -- typed environment contracts

Envlock lets you declare, validate, type, and document your environment variables from a single schema definition. Define your contract once with `defineEnv`, then call `loadEnv` at startup to get a fully typed configuration object or a clear error listing every missing or invalid variable. The CLI (`@envlock/cli`) adds CI checks, `.env.example` generation, and drift detection against `.env` files.

### Better together

Specdiff guards the API boundary between services; Envlock guards the configuration boundary between a service and its runtime. Together they close the two most common gaps where implicit contracts cause production incidents. Both are TypeScript ESM-only, MIT-licensed, and require Node.js 22 or later.

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

    Detect breaking changes in JSON Schema and OpenAPI documents with a 45-rule catalogue.

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

    Declare, validate, and document environment variables from a single typed schema.

#### [Quickstart](/quickstart)

    Install both tools and run your first comparison and validation in under five minutes.