New · April 2026

Spec-DrivenMode

Build features through living markdown contracts instead of chat scrollback. AGENTS.md + .specify/ give every AI tool you use the same project context. A title-bar status pill is the entire UI: click → grounded chat actions auto-send. The bundled coordinator skill drives constitution → specify → plan → tasks → implement, with a verifier subagent confirming the implementation still satisfies the spec at every step. Cross-compatible with GitHub Spec Kit, Cursor, Copilot CLI, Claude Code, OpenAI Codex, JetBrains Junie, Aider, Zed, and 30+ AGENTS.md-aware tools.

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Every artifact lands in the project as a real file you can read, edit and commit, in the GitHub Spec Kit layout other tools already understand.
The Spec-Driven Mode help dialog explaining the constitution, specify, plan, tasks, and implement workflow

Living Markdown Contracts, Not Frozen Specs

Per-feature `spec.md`, `plan.md`, and `tasks.md` evolve with the code. The verifier subagent re-checks each task against the spec the moment it's written, so drift surfaces while you can still steer, not in code review.

  • `.specify/specs/<NNN-feature>/` layout matches GitHub Spec Kit byte-for-byte
  • EARS-style acceptance criteria (`WHEN <trigger> THE SYSTEM SHALL <response>`)
  • On-demand drift report comparing acceptance criteria against the implementation

Cross-Tool by Default: AGENTS.md + Spec Kit

Files Plexon writes (`AGENTS.md` at the project root and `.specify/` for per-feature specs) are exactly what Cursor, Copilot CLI, Claude Code, OpenAI Codex, JetBrains Junie, Aider, Zed, and 30+ other tools already read. One project, every agent, no lock-in.

  • `AGENTS.md` auto-loaded into the system prompt in every mode (not just Spec)
  • `/speckit.specify`, `/speckit.plan`, `/speckit.tasks` all work on the same files
  • Pure markdown: no proprietary YAML, no JSON schema, human-editable
The Spec status pill open to a popover of grounded, one-click actions in the title bar

Title-Bar Status Pill, Not a Sidebar Panel

The Spec status pill in the title bar shows the active feature and phase at a glance. Click it for a popover menu of grounded actions: draft with AI, new feature, summarize state, advance phase, implement next task, drift report, update AGENTS.md / constitution. No sidebar real estate, no slash commands, no slash-command parser to learn.

  • Phase dot colour reflects spec / plan / tasks / implement / done
  • Help icon in the popover opens a dialog explaining the workflow
  • Inline "new feature" form: type a slug, hit Enter, the AI specs it
  • Comes with the Software Developer persona; any persona can turn it on under Settings → Appearance → Title bar

Live Status: No Polling, No Watcher

When the AI mutates the spec workspace through `plexon_spec`, the daemon pushes a `specChanged` notification with the new status payload and the pill updates instantly. There is no fsnotify watcher, no falling-edge poll, no manual refresh click, and no double-refresh on stream end. The eighth tool action, `refresh`, is the explicit escape hatch: any prompt that asks the AI to write a spec file through `plexon_write_file` ends with a `plexon_spec action=refresh` step so the pill still catches up.

  • Tool-side `OnChanged` callback fires after every successful mutation
  • Daemon notification → preload `daemon.onSpecChanged(cb)` → renderer state
  • Single authoritative event per mutation. UI never refreshes twice

Coordinator Skill Drives Phases, Subagents Implement

The bundled `spec-driven-development` skill walks the model through constitution → specify → plan → tasks → implement, asking clarifying questions at each phase. The implement step delegates to `subagent-driven-development`: an implementer subagent writes code, a spec-reviewer subagent (the verifier) confirms the result satisfies the spec, a quality-reviewer subagent enforces the constitution.

  • `plexon_spec` MCP tool with 8 actions (init, list, new, write, read, advance, toggle, refresh): single tool, no schema sprawl
  • Implement phase reuses the proven implementer→spec-reviewer→quality loop
  • `[P]` parallel markers fan out via the Parallel Agents Workspace

Why Spec-Driven Mode Matters

Cross-Tool Standard

Adopts the open AGENTS.md convention (60K+ repos, 30+ AI tools) and GitHub Spec Kit's `.specify/` layout. The same project remains drivable from Cursor, Copilot CLI, Claude Code, and any future agent tool that reads these conventions.

Verifier Subagent at Every Step

The implement phase routes each task through a spec-reviewer subagent that compares the output against `spec.md`. Spec drift surfaces immediately, while you can still steer, not after weeks of accumulated divergence.

Pill, Not a Panel

No sidebar real estate. The title-bar status pill shows initialization state + active feature + phase dot, and one click opens a context-aware menu. Every action stages a prompt and auto-sends: same gated send path the chat already uses.

Five Phases, One Tool

A single MCP tool (`plexon_spec`) with eight actions: init, list, new, write, read, advance, toggle, refresh. The bundled coordinator skill teaches the model when to invoke each: no slash-command registry, no schema sprawl, no mode-specific tool tables. The tool fires an `OnChanged` callback after every mutation so the title-bar pill updates from a single push notification: no polling, no fsnotify watcher.

Templates Inlined Into Prompts

When you click "Draft with AI", Plexon fetches the embedded AGENTS.md and constitution.md templates and inlines them verbatim in the prompt sent to the model. The output matches the structure byte-for-byte, with each blockquote placeholder replaced by grounded content from a quick codebase scan.

Reuses Proven Plumbing

Implement phase delegates to the existing `subagent-driven-development` skill (implementer → spec-reviewer → quality-reviewer). Parallel `[P]` tasks fan out through the existing Parallel Agents Workspace. New surface area is small; new behaviour is rich.

Connects to

Nothing here works alone. See the whole map for how the pieces fit together.

Where it goes

  • This extends AI Chat & Modes.

    A sixth mode, driven by living markdown contracts a verifier checks at every step.