SpecKit Companion adds a review layer to AI spec-driven development

AI coding agents are good at writing code from a spec. They're not good at telling you when the spec is bad. SpecKit Companion (alfredoperez.speckit-companion, v0.24.0) adds the missing layer: a VS Code extension that turns raw spec markdown into a reviewable, trackable pipeline before any agent burns a token on implementation. 1

The extension sits on top of GitHub's spec-kit — a CLI-driven spec-driven development (SDD) framework with 115k GitHub stars and support for 30+ AI coding agents. 2 Without a visual layer, spec-kit's outputs are plain markdown files in a specs/ directory: no progress indicator, no way to see what's planned vs. done, no inline review. SpecKit Companion is that visual layer.

Every spec moves through four stages: Specify (requirements and user stories) → Plan (architecture, data model, research) → Tasks (an implementation checklist with parallelism markers) → Done (archived or completed). SpecKit Companion renders each stage in a dedicated viewer panel — tabs at the top, a table of contents sticky on the left, Mermaid diagrams rendered inline, and action buttons at the bottom to advance the spec to the next stage. 1

The panel also shows a real-time Activity view: a Phases timeline with per-substep timing, an Approach card, a Tasks list, and a Review-comments rollup. This is where the "where did I leave off?" problem actually gets solved — you can see that Specify took 5m 52s, Plan took 3m, and Implement is still running at 14m 39s, all from the same panel.

The design principle behind the two-frontend model is worth noting: the viewer's action buttons and the CLI commands (e.g., /speckit.plan typed in the terminal) both write to the same spec files. As Alfredo Perez, the author, put it: "Neither 'owns' the workflow — they're two front-ends over one set of files." 3 That matters if you like typing commands but want a visual progress check without context-switching.

The extension's most immediately useful feature is inline review comments. Open any spec document in the viewer, click a line, and add a comment — the same interaction pattern as a GitHub PR review. Comments persist to .spec-context.json immediately (not on save, not on refine), so review progress survives editor restarts, machine switches, and teammates opening the same repo. 3

If the source file changes under a comment (lines shift, sections are edited), the comment re-anchors to the nearest matching heading rather than silently disappearing. When you're satisfied with the feedback, a Refine button sends all pending comments to the configured AI provider, which edits the spec file in place and marks the comments as applied. Applied comments stay in the history — they're not deleted.

The practical case for this: a spec requirement that says "users should be able to manage their profile" is vague enough to generate 200 lines of wrong code. Catching it at the spec stage with a comment — "what fields? what validation rules?" — takes 10 seconds. Fixing an agent's wrong implementation takes hours.

By default, spec-kit produces 8 documents per spec: spec.md, plan.md, tasks.md, plus research, data-model, contracts, quickstart, and architecture docs. That makes sense for a new auth system; it's overhead for a two-line config change. 4

Two opt-in beta settings address this:

Turbo Mode changes the shape of the spec. The same four-phase pipeline runs, but outputs are compressed: no user story scaffolding, tasks grouped by file and dependency, auxiliary documents generated on demand rather than by default. In Perez's own benchmark on a single feature, the full pipeline completed in 12.4 minutes vs. 21.3 minutes in standard mode — a 42% reduction — and the spec folder shrank from 8 files to 3. 4

Fast Path changes the route. For small changes (≤5 files, ≤10 tasks, no "rewrite/overhaul/new system" scope signals), Specify jumps directly to Implement, skipping Plan and Tasks entirely. The combined specify-and-implement run is merged into a single spec. As Perez described the guardrail: "It is best-effort, and it deliberately errs toward normal. A change never gets under-planned by accident." 4

Both are off by default. To enable:

// .vscode/settings.json
{
  "speckit.companion.templateProfile": "turbo",
  "speckit.companion.complexityFastPath": true
}

One caveat from Perez's own data: the Implement substep in Turbo mode was slightly slower (6.2m vs. 5.2m in standard). He called it out directly — the data doesn't support the intuition that more upfront design makes implementation faster. That kind of honest reporting in the build log is a good indicator of how the project is being run. 4

The extension dispatches spec commands to whichever AI agent you already use. Supported providers as of v0.24.0: Claude Code (terminal), Claude Code (VS Code panel via URI handler), Gemini CLI, GitHub Copilot CLI, Codex CLI, Qwen Code, OpenCode, and IDE Chat (auto-detects Copilot in VS Code, Composer in Cursor, Cascade in Windsurf). 3

The extension assembles the prompt and hands it to the CLI or the editor's built-in chat. It never reads the agent's response and never installs a CLI itself — those are prerequisites you bring. Each provider has a corresponding guidance file (CLAUDE.md, GEMINI.md, AGENTS.md, etc.) placed at the spec root to give the agent context on the workflow.

One provider-specific detail worth knowing: GitHub Copilot CLI in -p mode can't display interactive permission prompts in a VS Code terminal. The extension automatically switches Copilot to auto-approve mode at dispatch time to avoid silent hangs.

You can also define custom workflows via a .sdd.json config file, which lets you substitute an entirely different SDD methodology — including custom phases, command templates, and sub-document layouts.

SpecKit Companion shipped its first version on December 2, 2025 and reached v0.24.0 on June 15, 2026 — 24 minor versions in 6 months. The GitHub repo has 66 stars and 16 forks, with 428 commits, all from a single developer. 5

There's no third-party coverage yet — no Twitter/X discussion, no Hacker News threads, no Reddit posts specifically about this extension. The underlying spec-kit CLI has a larger community (a September 2025 r/GithubCopilot thread on spec-kit got 27 upvotes and 66 comments), but the Companion extension itself hasn't crossed over. 6

VS Code Marketplace install count is not publicly visible in the static page (dynamically loaded). The .vsix package is 1.17 MB — trimmed from 66.6 MB in an earlier build by removing dev fixtures and workspace caches from the package. 4

Free. MIT license. VS Code ≥ 1.84.0, macOS/Linux/Windows (including WSL). The extension works standalone (viewer + inline review) without the spec-kit CLI. The CLI extension is a separate install unlocked inside the extension's settings panel.

Install now if: you're already using spec-kit and want a visual pipeline view and inline review. Also worth trying if you're managing multiple parallel AI coding sessions and losing track of what's in progress vs. done.

Skip for now if: you don't use spec-kit or a compatible SDD workflow. The extension is a viewer and dispatcher for spec-kit's file structure — it won't do anything useful on a plain project without the CLI.