Most web applications today are static and built to serve broad user groups. Developers have limited time to address a long tail of niche user needs. Large language models can generate custom code that matches individual workflows, lowering the cost of creating personal tools.

Traditional software adds features that increase complexity for all users, making small‑specific functionality costly. Users need tools that can be tailored without bloating the core product. Sharing such custom tools remains difficult.

Embedding extensions directly into web services would require a runtime that is inexpensive to run, fast to start, and securely isolated. Each user execution must incur minimal cost, ideally fractions of a cent, and must avoid taking down the service or exposing keys. Limitations on CPU, memory, network traffic, and log volume are needed to prevent abuse. A capability model, where untrusted code receives only specific function references, can reduce the risk of data leakage.

Current implementations include platforms such as Salesforce, which has run user‑written code in a managed environment since 2007, and newer serverless frameworks like Cloudflare Workers that provide multi‑tenant execution, built‑in observability, durable workflows, and storage options. Technologies under evaluation include interpreters, V8 isolates, microVMs, and WebAssembly with WASI, each offering different trade‑offs in cost, speed, and isolation.

While the concept shows promise for enabling bespoke web applications, significant engineering work remains to define safe execution boundaries, enforce resource limits, and integrate with existing web infrastructure. The viability of large‑scale extensible software on the web will depend on progress in these technical areas.