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Glossary

Plain-language definitions for the terms shaping the modern stack. Each entry is short by design.

A

AI Harness
An AI harness is the software layer that surrounds a language model and turns it into an agent: it runs the model in a loop, executes the tools the model requests, manages what stays in the context window, and decides when the task is done. The common shorthand is Agent = Model + Harness.

D

E

Edge Runtime
An edge runtime is a JavaScript (and sometimes WebAssembly) execution environment that runs your code at CDN edge locations close to users instead of one central region. It uses lightweight V8 isolates or Wasm sandboxes rather than containers, giving near-zero cold starts but a constrained, web-standard API surface rather than full Node.js.

I

Islands Architecture
Islands Architecture is a web rendering pattern where a page is mostly static server-rendered HTML, with small isolated regions of interactive JavaScript (the islands) that hydrate independently on the client. Each island ships only the code it needs, leaving the rest of the page as plain HTML.

M

Model Context Protocol(MCP)
Model Context Protocol (MCP) is an open protocol, introduced by Anthropic in November 2024, that standardizes how AI applications connect to external tools, data, and prompts. It uses JSON-RPC 2.0 in a host-client-server architecture, where servers expose capabilities that clients discover and call over stdio or Streamable HTTP transports.

S

Signals
In UI frameworks, a signal is a reactive primitive: a value container that tracks who reads it and notifies its dependents when it changes, enabling fine-grained DOM updates without re-rendering whole component trees. It is unrelated to Unix process signals or the Signal messaging app.

W

WebMCP(WebMCP)
WebMCP is a browser API proposal that lets web pages expose JavaScript functions as structured tools to AI agents. Built on top of the Model Context Protocol, it replaces DOM scraping and screenshot-based interaction with explicit navigator.modelContext.registerTool() calls, giving agents named tools with JSON Schema inputs and same-origin scoping by default.