feature-builder

An agent that builds a to-do app feature from its state through its browser page, then passes it to a tester. State is the data an app currently remembers; the DOM is the browser's representation of a page.

In plain words
What is it for?
Use it to implement end-to-end features in a to-do app and hand the result to testing.
Why use it?
It coordinates implementation of a feature across both the app's data and visible interface.

Agent

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add agents/vishaljsoni/copilot-customizations-workshop/feature-builder
Clone the repo
git clone --depth 1 https://github.com/vishaljsoni/copilot-customizations-workshop
Per session 21 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 415 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin unknown No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00021 $0.00415
Opus 5 $0.00010 $0.00208
Sonnet 5 $0.00004 $0.00083
Haiku 4.5 $0.00002 $0.00042

Measured yesterday against content hash fc63bc682919, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

feature-builder scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured yesterday.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

solutions/lesson-02-final/.github/agents/feature-builder.agent.md · 33 lines

The source is not reproduced here

No licence file

A repository with no LICENSE is all rights reserved by default, so the body is not copied here. The metadata, the measurements and the link are.

Read it on GitHub

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. yesterday First seen · 33 lines · 21 tokens per session scan A fc63bc682919

Subscribe to this mod's changes

feature-builder is an agent published in the GitHub repository vishaljsoni/copilot-customizations-workshop (1 stars, last pushed 4mo ago), with no licence file. It adds 21 tokens to every session and 415 once invoked, about $0.0001 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.

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