What is mailsandbox CLAUDE.md?

Repository instructions for MailSandbox, a developer tool that captures test emails sent through SMTP and shows them in a web interface. It also provides a REST API for automation, with Go, Vue, and SQLite components.

Use them when starting MailSandbox, changing its SMTP or web ports, developing the interface, building it, or running focused Go tests.

They explain how to run the email-testing environment locally and which commands verify its backend and frontend.

mailsandbox CLAUDE.md — Instructions file for coding agents by btafoya: Repository instructions for MailSandbox, a developer tool that captu

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 instructions/btafoya/mailsandbox/claude-md

Clone the repo

git clone --depth 1 https://github.com/btafoya/mailsandbox

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

README.md

[![agentmods](https://agentmods.dev/badge/instructions/btafoya/mailsandbox/claude-md.svg)](https://agentmods.dev/instructions/btafoya/mailsandbox/claude-md)

Your own site

<a href="https://agentmods.dev/instructions/btafoya/mailsandbox/claude-md"><img src="https://agentmods.dev/badge/instructions/btafoya/mailsandbox/claude-md.svg" alt="Measured on agentmods" height="20"></a>

Per session 1,392 This file is loaded in full into every session.

When invoked 1,392 The same file — it is already loaded in full.

Security scan A 0 findings. Scan, not verified.

Origin original 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.

Model	Per session	Once invoked
Fable 5	$0.01392	$0.01392
Opus 5	$0.00696	$0.00696
Sonnet 5	$0.00278	$0.00278
Haiku 4.5	$0.00139	$0.00139

Measured 4d ago against content hash 3fb72e217e81, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

mailsandbox CLAUDE.md 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 4d ago.

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.

CLAUDE.md · 157 lines

How it starts

The opening of the file, as written. The whole thing — 157 lines — stays where its author put it; the contents beside it link to each section on GitHub.

CLAUDE.md

This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.

Project Overview

MailSandbox is an email and SMTP testing tool for developers. It captures emails via SMTP (port 1025), provides a web UI (port 8025) for viewing/testing, and includes a REST API for automation.

Tech Stack: Go 1.24.3 backend, Vue 3 + Bootstrap 5 frontend, SQLite storage, WebSockets for real-time updates

Essential Commands

Running MailSandbox

# Run locally with default settings
go run main.go

# Run with custom ports
go run main.go --smtp 0.0.0.0:1025 --ui 0.0.0.0:8025

Development Workflow

# Frontend development (watch mode)
npm install
npm run watch

# Build for production
npm run package
CGO_ENABLED=0 go build -ldflags "-s -w" -o mailsandbox

Testing

# Run Go tests for specific packages
go test ./internal/storage ./server -v

# Run all tests (use -p 1 to avoid parallel execution issues)
go test -p 1 ./internal/storage ./server ./internal/smtpd ./internal/pop3 ./internal/tools ./internal/html2text ./internal/htmlcheck ./internal/linkcheck -v

# Run a single test
go test ./internal/storage -v -run TestSpecificFunction

Code Quality

# Format Go code (REQUIRED before commits)
gofmt -s -w .

# Check Go formatting
gofmt -s -d .

# Lint JavaScript/Vue
npm run lint

# Fix JS/Vue linting issues
npm run lint-fix

Architecture

/internal/          - Private packages (core business logic)
  /smtpd/          - SMTP server implementation
  /storage/        - Database layer (SQLite/RQLite)
  /auth/           - Authentication logic
  /htmlcheck/      - HTML compatibility checking
  /linkcheck/      - Link validation
  /pop3/           - POP3 server (optional)
/server/           - HTTP server and API
  /apiv1/          - REST API v1 endpoints
  /ui-src/         - Vue.js source code
  /ui/             - Compiled/embedded UI assets
  /websockets/     - WebSocket handlers for real-time updates
/config/           - Application configuration
main.go            - Application entry point

Read the full file on GitHub · 157 lines

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.

4d ago First seen · 157 lines · 1,392 tokens per session scan A 3fb72e217e81

Subscribe to this mod's changes

mailsandbox CLAUDE.md is an instructions file published in the GitHub repository btafoya/mailsandbox (7 stars, last pushed 11mo ago), licensed MIT. It adds 1,392 tokens to every session, about $0.0070 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.

vscode buildNext.instructions.md

Working notes and architecture documentation for the new esbuild-based build system in build/next. Use when making changes to the new build pipeline (transpile/bundle commands, NLS plugin, source-map handling, resource copying, or self-hosting watch tasks).

microsoft/vscode · 6,785 tokens

mailsandbox CLAUDE.md