What is l123 CLAUDE.md?

Project instructions for developing a Lotus 1-2-3 clone, an old spreadsheet program with a text-based interface. It identifies the project documents to consult and requires test-first development.

Use it when changing the L123 project. It guides decisions using the specification, plan, and menu documents, then requires a failing test, the smallest passing change, and refactoring.

It gives the coding agent the project’s rules and source documents before changes are made, reducing the risk of implementing behavior that conflicts with the specification.

How duane1024/l123 configures Claude Code

Reuse

Borrowing it

Nothing to install: this file belongs to duane1024/l123. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.

Copy the file

curl -O https://raw.githubusercontent.com/duane1024/l123/master/CLAUDE.md

Clone the repo

git clone --depth 1 https://github.com/duane1024/l123

Made for: Claude Code.

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/duane1024/l123/claude-md/github.svg)](https://agentmods.dev/instructions/duane1024/l123/claude-md)

Your own site

<a href="https://agentmods.dev/instructions/duane1024/l123/claude-md"><img src="https://agentmods.dev/badge/instructions/duane1024/l123/claude-md/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

Your own site · 80×15

<a href="https://agentmods.dev/instructions/duane1024/l123/claude-md"><img src="https://agentmods.dev/badge/instructions/duane1024/l123/claude-md.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 2,255 This file is loaded in full into every session.

When invoked 2,255 The same file — it is already loaded in full.

Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.

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 5.1	$0.02255	$0.02255
Opus 5.5	$0.00902	$0.00902
Sonnet 5.5	$0.00451	$0.00451
Haiku 4.5	$0.00226	$0.00226

Measured 1mo ago against content hash bb3452da0d8c, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

l123 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 1mo 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 · 213 lines

How it starts

The opening of the file, as written. The whole thing — 213 lines — stays where its author put it; the contents beside it link to each section on GitHub.

CLAUDE.md — L123 project guide

Session-level conventions for working on L123 (a Lotus 1-2-3 R3.4a for DOS TUI clone). Living document — edit freely as conventions emerge.

Canonical docs — read these before making decisions

docs/SPEC.md — what L123 is. Scope, modes, menu tree, authenticity contract.
docs/PLAN.md — implementation milestones, risk register, test strategy.
docs/MENU.md — complete menu tree; source of truth for l123-menu.

If code and doc disagree, fix the doc first, then write code to match.

How we develop: red / green / refactor (strict TDD)

Test-first, always. Every change to shipping code follows this loop:

1. Red

Write the failing test(s) that describe the behavior you want. Run them. They must fail for the right reason — not a compile error, not a panic from unrelated setup. cargo test -p <crate> shows a clean failure in the new test, pointing at the behavior being specified.

If you can't figure out what the test should assert, the behavior isn't specified enough yet. Re-read SPEC, or write the acceptance transcript first, then come back.

2. Green

Write the minimum code to make the tests pass. No refactoring, no extra features, no speculative abstractions, no helpers you "might need later." If a test is green before you meant it to be, delete the extra code until only the test's claim is covered.

3. Refactor

Now, and only now, clean up. Re-run tests after every small refactor step. Never refactor with red tests. Clippy must stay clean: cargo clippy --workspace --all-targets -- -D warnings.

Exceptions (be honest — they should be rare)

Pure docs/comment changes.
Throwaway spikes — must be marked WIP: spike and deleted before landing. Any code you keep must have tests written before it.

Test tiers

Every feature lands with tests at one or more of:

Unit tests — colocated with source (#[cfg(test)] mod tests). Pure-function tests; no ratatui, no IronCalc.
Engine integration tests — crates/l123-engine/src/ironcalc_adapter.rs under #[cfg(test)]. Drive the Engine trait against real IronCalc.
Acceptance transcripts — tests/acceptance/*.tsv, run by crates/l123-ui/tests/acceptance.rs. Keystrokes in, on-screen state out. Every item in SPEC §20 "Authenticity Contract" gets ≥1 transcript before the claim can be called done.

Read the full file on GitHub · 213 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.

1mo ago Changed · +5 lines · +58 tokens per session bb3452da0d8c
2mo ago First seen · 208 lines · 2,197 tokens per session scan A 23dc72163c14

Subscribe to this mod's changes

l123 CLAUDE.md is an instructions file published in the GitHub repository duane1024/l123 (130 stars, last pushed 1mo ago), licensed MIT. It adds 2,255 tokens to every session, about $0.0090 per session on Opus 5.5. 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 2026-08-30.

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 · 9,715 tokens

l123: Instructions file for Claude Code