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01 / Design layer for agent harnesses

Tell Proof

Tell sits beside Cursor as an independent design runtime. The authoring agent proposes. Tell measures, critiques, redesigns, and verifies. Humans stay in control.

2026 · Open source · local dogfood

Tell Proof product still: capture, named tells, and a before/after seam
Problem
Coding agents compile. They still ship the same generated look: system fonts, violet accents, shadow on every card. The harness grades its own homework.
Approach
An independent critic beside Cursor. Playwright captures the rendered page. Fourteen detectors name genericness and drift. Direction becomes a reviewable patch. Proof runs in a disposable checkout.
Shipped
Next.js monorepo, MCP tools, Studio skill graph, and a captioned product demo. Open source. Local dogfood. No public production host claimed here.

The gap

Ask an agent to make a page prettier and you usually get the same defaults again. That is not a failure of effort. The harness is optimized for compiling code and local file edits. Production UI needs composition, contrast, token rhythm, and an independent proof loop.

Tell is the missing design layer for agent-built software. It is not a replacement for a11y, security, or functional tests. It is the visual evidence most harnesses still skip.

The loop

Observe: Playwright captures the page users actually see, plus computed styles, tokens, and state probes.

Name: fourteen deterministic detectors call out system fonts, radius monotony, shadow overuse, gray mush, token bypasses, and more.

Direct: voice or text art-direction becomes a preset and concrete action items. Repair: source-ranked diffs, never silent auto-apply. Prove: a disposable checkout recaptures before and after so the harness can trust the fix.

What is on disk

A pnpm monorepo: Next.js report and Studio UI, a shared engine, and an MCP server with eleven tell_* tools. Deterministic capture and detectors run without a model. Models only help where language helps.

The in-repo demo video walks capture, named tells, the seam, voice direction, a draft Cursor patch, then Studio specimens. I dogfood Tell on itself. There is no public live product URL on this site because the honest home is the repository.

Tell Report naming fourteen detector findings on a captured page
Tell Report naming fourteen detector findings on a captured page
Before and after seam comparing a generic capture to a reconciled editorial pass
Before and after seam comparing a generic capture to a reconciled editorial pass

Clone it, run it locally, point it at a bland fixture. The point is a receipt, not a vibe.

  • Next.js
  • TypeScript
  • MCP
  • Playwright
  • pnpm
ashishpatill/tell-proof