implementing-contract-first

implementing-contract-first is a skill for Claude Code, Codex from Nolane-x/forge-os. It costs 32 tokens per session (179 once invoked), scanned A, original, MIT.

A set of instructions for starting implementation by defining the required contract. A contract is the agreed input, output, and behavior that software must satisfy.

In plain words
What is it for?
Use it when building software that must follow explicit interfaces or behavior rules and needs typed conditions, evidence, and coverage.
Why use it?
It reduces misunderstandings by making requirements and boundaries clear before implementation decisions are made.

Skill for Claude CodeCodex

Part of the forgeos plugin — 56 skills, 1 command, 1 agent, 1 MCP server shipped together

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 skills/nolane-x/forge-os/implementing-contract-first
Any agent
npx skills add Nolane-x/forge-os --skill implementing-contract-first
Clone the repo
git clone --depth 1 https://github.com/Nolane-x/forge-os

Made for: Claude Code, Codex.

Or install forgeos, the plugin that ships this one along with the rest of its 56 skills, 1 command, 1 agent, 1 MCP server.

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.

agentmods badge for implementing-contract-first

README.md
[![agentmods](https://agentmods.dev/badge/skills/nolane-x/forge-os/implementing-contract-first.svg)](https://agentmods.dev/skills/nolane-x/forge-os/implementing-contract-first)
Your own site
<a href="https://agentmods.dev/skills/nolane-x/forge-os/implementing-contract-first"><img src="https://agentmods.dev/badge/skills/nolane-x/forge-os/implementing-contract-first.svg" alt="Measured on agentmods" height="20"></a>
Per session 32 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 179 The whole file, excluding the scripts and references it only reads on demand.
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.

ModelPer sessionOnce invoked
Fable 5 $0.00032 $0.00179
Opus 5 $0.00016 $0.00089
Sonnet 5 $0.00006 $0.00036
Haiku 4.5 $0.00003 $0.00018

Measured 3d ago against content hash 5573e4ad0bc1, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

implementing-contract-first 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 3d 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.

skills-v2/l1/implementation/implementing-contract-first/SKILL.md · 23 lines

What it actually says

Implementing Contract First

Core principle

Implementing contract first within implementation lifecycle boundaries. Deterministic checks own scope, typed preconditions, evidence, and coverage; the agent performs only the domain judgment that cannot be encoded safely.

Do not activate when

  • the requested outcome does not require implementing contract first within implementation lifecycle boundaries
  • the typed inputs for implementing-contract-first are absent and another technique owns the outcome
Files

What ships with it

9 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.

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. 3d ago First seen · 23 lines · 32 tokens per session scan A 5573e4ad0bc1

Subscribe to this mod's changes

implementing-contract-first is a skill published in the GitHub repository Nolane-x/forge-os (10 stars, last pushed 1mo ago), licensed MIT. It adds 32 tokens to every session and 179 once invoked, about $0.0002 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.