My Visionaire MCP verifies whether agent CSS fixes rendered

Visionaire MCP v0.7 introduces a verification layer that lets AI coding agents visually inspect live web pages, identify the exact CSS rule, file, and line causing rendering bugs, and verify fixes automatically. The tool addresses the problem of LLMs being "structurally blind" to rendered output, reducing the need for developers to manually explain visual issues.

Which rule, which file, which line — and why it wins. The problem: Something looks off. You screenshot it, explain it, the LLM guesses wrong, you re-explain. The solution: Visionaire reads the live page and hands the LLM the exact rule, file, and line. Right fix, first try. You shouldn't have to write a paragraph to explain a 2px margin bug — and now you don't. Less explaining, more fixing: built for developers, vibe coders, and anyone shipping site design changes with an LLM in the loop. Status: v0.7 — 28 tools, 435 tests 252 unit + 183 end-to-end on real Chrome , a 24-case seeded-bug benchmark npm run bench , verified live against wordpress.org. What's new, by version v0.7 — the verification layer: assert visual a 17-type assertion grammar — PASS/FAIL verdicts with measured pixels, offending uids, and re-runnable named suites , visual diff pixel diff vs a mockup or recorded baseline, divergent regions mapped to element uids , impact preview blast radius + sandboxed dry-run before editing a shared selector , diagnose ranked "why is this broken" culprits with measured evidence , responsive sweep one call → per-viewport verdict matrix , capture proof before/after evidence bundles with a verdict delta ; the verify-after-edit harness for Claude Code and Cursor npx visionaire-engine init-harness ; style diff { capture pixels } baselines; check alignment deprecated in favor of assert visual v0.6 — the pixel-perfect pack: check alignment group alignment / gap-rhythm / grid / pixel-snap audit and pick color actual painted-pixel sampling + WCAG contrast verdicts v0.5: inject css — the live fix loop trial a fix on the page, see what changed, converge, write source once ; navigate { bypassCache } for stale-stylesheet hard reloads; blast-radius + scoped-fix reporting on explain styles change the button, not all buttons v0.4 field-report items : interact to drive the UI into a state and inspect it; measure element for sub-pixel glyph/text-ink centering; an evaluate escape hatch; element-scoped crops/zoom on annotated screenshot ; match:"any" / visibleOnly:false on find elements ; zero-config cold-start Chrome discovery v0.3: the time dimension — event-listener attribution, animation diagnosis, source-attributed interaction timelines Hardened for untrusted pages: prompt-injection sanitization, fail-fast watchdog, dialog auto-dismiss AI coding agents are structurally blind to what they render. They emit CSS as text and never see the pixels that come back — so they guess, insist the guess worked, and loop. The community has a name for it now: "CSS gaslighting." Visionaire gives the agent deterministic eyes on the real render — measured geometry, the actual cascade winner, PASS/FAIL verdicts — so the loop ends. If you want the problem in other people's words first, start here: - — Adam Argyle on why models can't reason about layout they can't perceive. Why AI Sucks At Front End https://nerdy.dev/why-ai-sucks-at-front-end "It's an LLM, not a rendering engine It's notoriously bad at math, and throwing screenshots at it means very little. It's stabbing in the dark." - — Mauro Bieg on the wider cost of AI-generated frontend. Is AI Causing a Repeat of Frontend's Lost Decade? https://mastrojs.github.io/blog/2026-05-23-is-AI-causing-a-repeat-of-frontends-lost-decade/ "AI is enabling lots of AI slop — but this doesn't mean we don't still need people who know what they're doing." Ask an LLM to fix a visual bug today and it gets one of two incomplete pictures: pixels, with no link back to code, or code, with no rendering truth about what's actually winning on screen. Existing browser MCPs make this worse for design work specifically — they ship accessibility snapshots that deliberately strip out all styling. What's missing is explanation and attribution : Which CSS rule wins the cascade for this property, and why did the others lose? Which file, which line does the winner live in — or which Elementor widget control, or which Customizer entry? Why is this element invisible, misaligned, or the wrong size? Visionaire answers those questions with zero AI inside — everything is computed deterministically from the Chrome DevTools Protocol plus closed rulesets. The fuzzy part matching "the button under the hero looks off" to an actual element stays with the calling LLM, which gets uid-keyed snapshots, search tools, and annotated screenshots to do that cheaply. Live against wordpress.org: why color = rgb 255, 255, 255 : WINNER class =wp-block .wp-block-button link { color: var --wp--custom--button--color--text } spec 0,2,0 → themes/wporg-parent-2021/build/style.css:499 line | theme: wporg-parent-2021 — edit themes/wporg-parent-2021/build/style.css lost specificity :root :where .wp-element-button, .wp-block-button link { color: fff } spec 0,1,0 → global-styles-inline-css:2 db-entity | Global Styles — Site Editor → Styles theme.json / wp global styles lost origin a:-webkit-any-link { color: -webkit-link } spec 0,1,1 → user-agent stylesheet Winner, losers with the decisive loss reason, and an honest edit pointer for each — including WordPress-aware answers like "Site Editor → Styles" instead of a useless path to a generated file. Requires Node ≥ 20 and Chrome/Chromium installed. Fastest path — register straight from npm with Claude Code no clone, no build : claude mcp add visionaire -- npx -y visionaire-engine Or run from a clone for development or a pinned local build : git clone https://github.com/mi60dev/visionaire-engine && cd visionaire-engine npm install && npm run build claude mcp add visionaire -- node "$PWD/dist/index.js" Using GitHub Copilot, Cursor, Claude Desktop, Google Antigravity , or another client? See docs/clients.md for a copy-paste config for each, plus browser-install help for Linux/WSL/Docker. Run it from your project's root directory — Visionaire is at its best when the agent has both the running site and its source on disk, so it can cross-reference the two. Ground before you search: take a page snapshot or read the source to get real element names instead of guessing selectors. If a selector matches nothing, the error suggests the closest real ids/classes on the page. Then, in a session: connect { url: "https://your-site.com" } — launches Chrome or { browserUrl: "http://127.0.0.1:9222" } to attach to your real, logged-in browser page snapshot {} — a uid-keyed census of what's visible; target elements by their , not invented selectors uid explain styles { uid: "e17", property: "margin-bottom" } — cascade verdict with file:line Try it without an MCP client: npm run demo bundled fixture npm run demo -- https://wordpress.org --selector "a.wp-block-button link" Session & grounding — get connected and find the right element without guessing. | Tool | Purpose | |---|---| connect / navigate / set viewport | Launch or attach to Chrome, go to a URL bypassCache for hard reloads , emulate viewports | page snapshot | Pruned, uid-keyed tree of what's visible — geometry, layout hints, invisibility reasons | page origins | Stylesheet inventory + platform detection WordPress version, theme, builders, optimizers | find elements | Deterministic search by text, selector, role, or screen region — AND-combined by default, match:"any" for a union, visibleOnly:false to include hidden elements | node at point | x,y → element uid + ancestor chain | pick element | Human-in-the-loop grounding: DevTools-style hover highlight, the user clicks the element that looks wrong | Explanation — the "why," with a receipt. | Tool | Purpose | |---|---| inspect element | The "what": box model, computed values, visibility verdict | explain styles | The wedge. Cascade winner/loser per property with file:line + origin attribution, each winner's blast radius how many other elements it styles , and a scoped-fix selector for just this element | inspect ancestors | Constraint-chain walk: which ancestor constrains width/overflow/stacking | get listeners | Event listeners on an element + its ancestors, with handler file:line and capture/passive/once flags | explain animations | Animations/transitions touching an element: live census, declared rules with file:line, and a closed "why is it not smooth" ruleset | Pixel-level checks — new in v0.6. | Tool | Purpose | |---|---| measure element | Sub-pixel rendered geometry: content box + true text-ink box glyph extents with a centering verdict — "is this × actually centered?" | check alignment | deprecated → Group pixel audit: which of N elements is off-alignment by how many px, gap-rhythm outliers, size consistency, N-px grid conformance, pixel-snap warnings assert visual | pick color | The actual painted pixel composited truth: gradients, images, opacity + computed colors + WCAG AA/AAA contrast verdict | Interaction & time — states, not just snapshots. | Tool | Purpose | |---|---| interact | Drive the UI into a state open a menu/popup/modal, reveal a tab and leave it there so you can inspect the new state — reports post-action visibility + box | record interaction | One interaction → a source-attributed causal timeline: handlers, mutations, cancelled transitions, layout shifts | Fixing & verifying | Tool | Purpose | |---|---| inject css | The live fix loop: trial declarations on an element or a page-wide rule without touching source — see what changed, converge, write source once, revert | style diff | Record styles, compare later — verify-my-fix loops | evaluate | Escape hatch: run agent-authored JavaScript in the page and get the JSON result, for the genuinely bespoke case no other tool covers | annotated screenshot | Screenshot with numbered marks that equal snapshot uids — or an element-scoped crop via clipTo with padding / scale zoom and optional annotate:false | Verification & proof — new in v0.7. | Tool | Purpose | |---|---| assert visual | The verification gate. State rendered-geometry claims equal heights, alignment, gaps, clipping, colors, z-order — 17 assertion types → deterministic PASS/FAIL with measured pixels and offending uids; register named suites and re-run them after every edit | visual diff | Pixel-diff the live page or one element against a mockup PNG or a recorded baseline — MATCH/DIVERGENT with divergent regions mapped back to element uids, optional heatmap artifact | impact preview | Blast-radius report before editing a shared selector: who else matches, grouped with uids, plus a sandboxed dry-run predicting exactly which elements would change | diagnose | One-shot "why does this look broken" — ranked culprits with measured evidence for clipping, overflow, off-center, invisibility, overlap, wrong size | responsive sweep | One verification payload across many viewports → a per-viewport verdict matrix "fixed on desktop, still broken on mobile" caught in one call | capture proof | Before/after evidence bundles: annotated screenshots + suite verdicts, with a verdict delta proving the fix flipped FAIL → PASS | Full reference: docs/tools.md /mi60dev/visionaire-engine/blob/main/docs/tools.md An agent edits a stylesheet, reads its own diff, and declares "now the cards are equal height" — without ever seeing a rendered pixel. Visionaire gives your agent deterministic eyes on rendered truth. The loop: Preview shared-class blast radius → impact preview . Edit the smallest change. Assert your claim → assert visual or re-run a named suite id . You get PASS/FAIL + the actual measured pixels + the offending element uids. Diagnose any FAIL → diagnose returns the ranked culprit with evidence. Sweep responsive → responsive sweep returns a per-viewport verdict matrix. Prove it → capture proof bundles before/after screenshots + verdict delta. Real output — the same suite before and after a fix: { "verdict": "FAIL", "summary": "1 assertion: 0 PASS, 1 FAIL — registered as suite 'cards' re-run with just {\"suite id\":\"cards\"} ", "results": { "type": "equal height", "verdict": "FAIL", "id": "cards-equal", "measured": { "values": 412, 388 , "unit": "px", "delta": 24, "tolerance px": 1 }, "offending uids": "e1", "e2" } , "truncated": false, "suite id": "cards" } …fix the CSS, re-run with just { "suite id": "cards" } : { "verdict": "PASS", "summary": "1 assertion: 1 PASS, 0 FAIL", "results": { "type": "equal height", "verdict": "PASS", "id": "cards-equal", "measured": { "values": 412, 412 , "unit": "px", "delta": 0, "tolerance px": 1 } } , "truncated": false, "suite id": "cards" } Run npx visionaire-engine init-harness from your project root to wire the included Claude Code hooks or Cursor rule so the agent physically cannot end a turn claiming "it's fixed" without a verification pass on record. How the markers, hooks, and Stop gate work: docs/harness.md /mi60dev/visionaire-engine/blob/main/docs/harness.md . docs/clients.md /mi60dev/visionaire-engine/blob/main/docs/clients.md — install in Claude, Copilot, Cursor, Antigravity, and other MCP clients docs/tools.md /mi60dev/visionaire-engine/blob/main/docs/tools.md — tool-by-tool reference with real examples docs/harness.md /mi60dev/visionaire-engine/blob/main/docs/harness.md — the verify-after-edit harness hooks, markers, init-harness docs/architecture.md /mi60dev/visionaire-engine/blob/main/docs/architecture.md — how the deterministic pipeline works docs/wordpress.md /mi60dev/visionaire-engine/blob/main/docs/wordpress.md — WordPress origin resolution guide docs/development.md /mi60dev/visionaire-engine/blob/main/docs/development.md — building, testing, extending No internal LLM — deterministic, cacheable, testable, host-agnostic. Fuzzy grounding belongs to the calling LLM ; we make it cheap. Complement the incumbent browser MCPs same uid idiom , don't compete. Honesty ladder on every attribution: line file db-entity component generated unknown . Token-budgeted output — a dossier is 300–800 tokens, never a dump. Visionaire is pointed at arbitrary, untrusted pages, so it treats page content as hostile: Prompt-injection defense. Page-derived strings element text, class names, ids, attribute values are sanitized at the single choke point where they enter tool output — collapsed to one line, stripped of control and bidirectional-override characters, and length-capped. A page cannot smuggle instruction-shaped text formatted as a "system message" toward the calling LLM; such content can only appear as an inert, quoted, truncated fragment. Fail-fast, never hang. Every tool call is wrapped in a watchdog default 60s, VISIONAIRE TOOL TIMEOUT MS to override; pick element / record interaction get their declared wait plus slack . A wedged browser returns an actionable error telling you to connect again, instead of blocking the client. No dead-locking dialogs. Page alert / confirm / prompt calls are auto-dismissed — otherwise they would block every evaluate-family CDP call indefinitely. Visionaire never executes page-authored code as instructions; it only reads and attributes. The calling LLM should still treat tool output as data about a page, not as commands. - Chromium-only CDP is the only path to matched-rule source locations; getMatchedCSSRules was removed from browsers years ago . @layer : unlayered-vs-layered ordering is exact; ordering between two different layer chains is a deterministic proxy CDP doesn't expose layer declaration order .- Some CDP fields we rely on specificity , layers are experimental; the engine feature-detects them and falls back e.g. to its own specificity parser , and a contract smoke test in test/e2e.test.ts fails loudly if a Chrome update breaks the core protocol shape the experimental fields are logged as present/absent . Visionaire is free and open source. If it saves you time and you'd like to help keep development going, you can chip in on Ko-fi https://ko-fi.com/mishonyai or Patreon https://www.patreon.com/cw/MishonyAI . Completely optional, and genuinely appreciated. Bug reports and field notes help just as much — see CONTRIBUTING.md /mi60dev/visionaire-engine/blob/main/CONTRIBUTING.md . Apache License 2.0 — free for everyone, including commercial use, with a patent grant. Copyright © 2026 mi60dev NOTICE /mi60dev/visionaire-engine/blob/main/NOTICE . Built and maintained by @mi60dev https://github.com/mi60dev . Contributions welcome under the Apache-2.0 terms — see CONTRIBUTING.md /mi60dev/visionaire-engine/blob/main/CONTRIBUTING.md .