leyline

Leyline

An opinionated developer-session workflow plugin for Claude Code, Cursor, Codex, OpenCode, GitHub Copilot CLI, and Gemini CLI.

Leyline encodes one coherent developer session from first message to merged branch as a deterministic pipeline of skills that hand off to each other in a fixed order. Every stage has an entry gate, a verifiable output, and an explicit successor. No stage silently skips. No completion claim ships without evidence. The iron laws are enforced at every handoff.

First-response rule

Before any response or action - including clarifying questions - check whether any Leyline skill applies. If one does (probability >= 1%), invoke it before narrating. If none does, name the skills you considered and why you rejected each.

This rule is the single highest-leverage instruction Leyline ships. It appears verbatim in CLAUDE.md, AGENTS.md, GEMINI.md, and skills/using-leyline/SKILL.md so every load path delivers it to the agent. Drift between files is caught by scripts/check-manifests.sh.

What Leyline gives you

• A full development pipeline. Eight stages covering Discovery, Interrogate, Isolate, Plan, Execute, Discipline, Review, and Finish. Each stage's skill names its successor; nothing improvises.
• Five iron laws enforced as code. TDD, systematic debugging, verification-before-completion, design-driven-development, and accessibility-verification are not suggestions — they are hard gates that block downstream work when violated.
• Fresh-subagent review per task. Stage 5 dispatches a new subagent per task with up to four review passes (spec, quality, design when surfaces are touched), then hands off to Stage 7 for branch-level review with bias-free reviewer agents. Each subagent receives constructed context only.
• Verifiable markers at every stage boundary. Specs carry approval markers, plans reference spec rounds, baselines record worktree state, review logs carry completion markers. Downstream stages grep for markers; session-state promises do not pass.
• Tool-agnostic accessibility and design review. Harness-aware subagents use browser automation, a11y scanners, design-tool MCPs when present; fall back to structural review when absent. Zero runtime dependencies.
• A meta-skill for contributors. writing-skills enforces TDD-for-prose: baseline pressure test, write minimal rebuttal, verify, refactor. Every skill change requires traces.

Pipeline at a glance

Human partner: "let's build X"
        |
        v
  [1] Discovery ........... brainstorming + design-brainstorming
        |                   approved product + UX specs
        v
  [2] Interrogate ......... deep-discovery + design-interrogation
        |                   100-question pressure tests; loop back on material revisions
        v
  [3] Isolate ............. using-git-worktrees
        |                   isolated branch workspace, green baseline
        v
  [4] Plan ................ writing-plans
        |                   2-to-5-minute tasks with exact paths, code, verification
        v
  [5] Execute ............. subagent-driven-development OR executing-plans
        |                   fresh subagent per task + up to 4 review passes
        v   <-- governed by [6] Discipline overlays:
        |       Code: TDD, systematic-debugging, verification-before-completion
        |       Experience: design-driven-development, accessibility-verification
        v
  [7] Review .............. requesting/receiving-code-review (+ design when surfaces)
        |                   code-reviewer and design-reviewer subagents
        v
  [8] Finish .............. finishing-a-development-branch
        |                   merge / PR / keep / discard
        v
  Pipeline terminates with evidence trail in docs/leyline/

Install

Install commands for each supported harness. All paths resolve against github.com/forsonny/leyline.

Claude Code

/plugin marketplace add forsonny/leyline
/plugin install leyline@leyline-marketplace

The first command registers this repo as a marketplace via .claude-plugin/marketplace.json. The second installs the plugin it lists.

Cursor

Cursor consumes Claude Code-compatible plugins. Use the same marketplace add-and-install flow in Cursor's plugin interface, pointing at https://github.com/forsonny/leyline.

GitHub Copilot CLI

copilot plugin marketplace add https://github.com/forsonny/leyline
copilot plugin install leyline

Gemini CLI

gemini extensions install https://github.com/forsonny/leyline

Codex

codex plugin marketplace add forsonny/leyline