Your AI agent burns ~50,000 characters of accessibility tree just to look at the Hacker News front page. Charlotte does it in 364.
Charlotte is an MCP server that gives AI agents structured, token-efficient access to the web.
Instead of dumping the full accessibility tree on every call, Charlotte returns only what
the agent needs: a compact page summary on arrival, targeted queries for specific elements,
and full detail only when explicitly requested. On content-heavy pages that orientation is
up to ~140x smaller than a full accessibility-tree snapshot from ; on trivially small pages the two are roughly the same size.
Renders web pages into structured, agent-readable representations using headless Chromium.
Most browser MCP servers dump the entire accessibility tree on every call — a flat text blob that can exceed a million characters on content-heavy pages. Agents pay for all of it whether they need it or not.
Charlotte decomposes each page into a typed, structured representation — landmarks, headings, interactive elements, forms, content summaries — and lets agents control how much they receive with three detail levels. When an agent navigates to a new page, it gets a compact orientation (364 characters for Hacker News) instead of the full element dump (~50,000 characters). When it needs specifics, it asks for them.
Benchmarks
Measured on Charlotte v0.8.0 against Playwright MCP v0.0.79, by characters returned per tool call on real websites (npx tsx benchmarks/run-benchmarks.ts --suite comparison), 2026-08-08. This section is a summary — the canonical benchmarks page (including per-task cost and release drift) is charlotte.mintlify.site/benchmarks; methodology, instruments, and raw results: benchmarks/.
Orientation cost (what an agent pays to "see" a page on arrival):
A Charlotte navigate returns a usable orientation by default — landmarks, headings, and interactive element counts grouped by page region. To get the equivalent with Playwright MCP, an agent calls browser_snapshot, which returns the full accessibility tree. (Playwright's browser_navigate alone returns only a short confirmation, not the page content, so it isn't a like-for-like comparison.)
Site
Charlotte navigate
Playwright browser_snapshot
Smaller by
example.com
415
465
1.1x
httpbin form
619
1,847
3.0x
GitHub repo
3,778
38,983
10x
Wikipedia (AI article)
22,134
1,137,928
51x
Hacker News
364
50,706
139x
The advantage scales with page complexity: on content-heavy pages the structured orientation is ~10–140x smaller than the full snapshot, while on a trivially small page like example.com the two are within ~20% of each other (and on a page that small, the structured representation can be the larger of the two — there is simply nothing to summarize away). Charlotte's value shows up precisely where Playwright's flat dump hurts most. When an agent needs more than the orientation, it calls observe or find for exactly the part it wants instead of paying for the whole tree up front.
Tool definition overhead (invisible cost per API call):
Profile
Tools
Def. tokens/call
Savings vs full
full
43
8,500
—
browse (default)
23
4,372
~49%
core
7
2,186
~75%
Tool definitions are sent on every API round-trip. With the default browse profile, Charlotte carries ~49% less definition overhead than loading all 43 tools; the minimal core profile cuts it by ~75%. See the profile benchmark report for full results.
The workflow difference: A Playwright agent that reads the full snapshot receives ~50,000 characters every time it looks at Hacker News, whether it's reading headlines or hunting for a login button. A Charlotte agent gets 364 characters on arrival, calls find({ type: "link", text: "login" }) to get exactly what it needs, and never pays for the rest.
How It Works
Charlotte maintains a persistent headless Chromium session and acts as a translation layer between the visual web and the agent's text-native reasoning. Every page is decomposed into a structured representation:
Agents receive landmarks, headings, interactive elements with typed metadata, bounding boxes, form structures, and content summaries — all derived from what the browser already knows about every page.
Features
Navigation — navigate, back, forward, reload
Observation — observe (3 detail levels, structural tree view), find (spatial + semantic search, CSS selector mode, output_file for large result sets), screenshot (with persistent artifact management), screenshots, screenshot_get, screenshot_delete, diff (structural comparison against snapshots)
Interaction (iframe-aware) — click, click_at (coordinate-based), type (with slow typing support), select, toggle, submit, scroll, hover, drag, key (single/sequence with element targeting), wait_for (async condition polling), upload (file input), fill_form (batch form fill), dialog (accept/dismiss JS dialogs)
Session Management — tabs, tab_open, tab_switch, tab_close, viewport (generic presets or named devices such as "iPhone 15" with DPR, touch, and user agent emulation), network (throttling, URL blocking), set_cookies, get_cookies, clear_cookies, set_headers, configure
Development Mode — dev_serve (static server + file watching with auto-reload), dev_inject (CSS/JS injection), dev_audit (a11y, performance, SEO, contrast, broken links)
Utilities — evaluate (arbitrary JS execution in page context)
Tool Profiles
Charlotte ships 43 tools (42 registered + the charlotte_tools meta-tool), but most workflows only need a subset. Startup profiles control which tools load into the agent's context, reducing definition overhead by up to ~75%.
charlotte --profile browse # 23 tools (default) — navigate, observe, interact, tabs
charlotte --profile core # 7 tools — navigate, observe, find, click, type, submit
charlotte --profile full # 43 tools — everything
charlotte --profile interact # 31 tools — full interaction + dialog + evaluate
charlotte --profile develop # 34 tools — interact + dev_serve, dev_inject, dev_audit
charlotte --profile audit # 14 tools — navigation + observation + dev_audit + viewport
Agents can activate more tools mid-session without restarting:
charlotte_tools enable dev_mode → activates dev_serve, dev_audit, dev_inject
charlotte_tools disable dev_mode → deactivates them
charlotte_tools list → see what's loaded
Self-Hosting (Charlotte Remote)
Run Charlotte as a remote MCP server and connect it to claude.ai — one command:
docker run --cap-add SYS_ADMIN --shm-size 2g -p 3737:3737 ghcr.io/ticktockbent/charlotte
It prints a public connector URL and an operator token. In claude.ai:
Settings → Connectors → Add custom connector — paste the URL, leave the
OAuth Client ID/Secret fields blank, and enter the token on Charlotte's consent
page when it appears. That's it; you're browsing.
The demo URL and token are ephemeral (both rotate on restart). Running it for
real — stable domain, your own tunnel or reverse proxy, docker compose:
Self-Hosting. Trust model and
network guards: Security. Container
and sandbox internals: Docker.
See docs-internal/mcp-setup.md for the full setup guide, including development mode, generic MCP clients, verification steps, and troubleshooting.
Configuration
Charlotte resolves settings from four sources, highest precedence first: CLI arguments → environment variables → config file → built-in defaults. See docs/configuration.md for the complete reference.
Config file
Pass a JSON config file with --config, or drop a charlotte.config.json in the working directory and Charlotte loads it automatically:
Every section is optional; an empty {} is valid. The file is validated with zod — unknown keys, wrong types, or invalid enum values produce a clear startup error on stderr and Charlotte exits non-zero. Four settings also have environment variables: CHARLOTTE_NO_SANDBOX, CHARLOTTE_OUTPUT_DIR, CHARLOTTE_CDP_ENDPOINT, and CHARLOTTE_INIT_SCRIPT. Scripts that should run on every new document before page JS go in browser.initScripts or --init-script <path> (repeatable); see Init scripts.
The Chromium sandbox is on by default
v0.7.0 behavior change: Earlier releases baked --no-sandbox into every Chromium launch. As of v0.7.0 the Chromium sandbox is enabled by default — the primary defense between an untrusted page and the account Charlotte runs as. You must opt out explicitly where the kernel sandbox is unavailable.
charlotte --no-sandbox # CLI flag
CHARLOTTE_NO_SANDBOX=1 charlotte # environment variable
# or "browser": { "noSandbox": true } in the config file
Migration note (Docker / bare-metal): Containers usually cannot set up the kernel sandbox, so the provided Dockerfiles set CHARLOTTE_NO_SANDBOX=1 for you, and docker-compose.yml now keeps Docker's default seccomp filter (it no longer runs seccomp=unconfined). If you run Charlotte bare-metal as root, Chromium refuses to launch with the sandbox enabled — run as a non-root user (recommended) or pass --no-sandbox. Existing setups that previously relied on the implicit --no-sandbox and run in an environment where the sandbox can't initialize must now set CHARLOTTE_NO_SANDBOX=1 (or the flag/config equivalent) to keep working.
Running Charlotte Remote (HTTP mode) over the network raises additional trust-boundary and network-guard questions beyond the sandbox — see Security.
Output-size limits
The limits.* keys bound how much a single tool response can return so a pathological page (100k links, an infinite-scroll feed, a giant document body) cannot overflow the agent's context window. When a page response exceeds maxResponseBytes it degrades to a compact summary and suggests writing the full result to disk via output_file; charlotte_evaluate results are capped independently by maxEvaluateBytes. Truncated responses carry a truncation marker. See docs/configuration.md for the keys and defaults.
Crash recovery
A Chromium crash no longer wedges the server. The next tool call automatically relaunches the browser, clears the dead tab and CDP-session caches, and opens a fresh blank tab — so an agent can keep working after a renderer crash without restarting the MCP server.
Usage Examples
Once connected, an agent can use Charlotte's tools:
Browse a website
navigate({ url: "https://example.com" })
// → 612 chars: landmarks, headings, interactive element counts
find({ type: "link", text: "More information" })
// → just the matching element with its ID
click({ element_id: "lnk-a3f1c2" })
Charlotte returns structured representations with three detail levels that let agents control how much context they consume:
Minimal (default for navigate)
Landmarks, headings, and interactive element counts grouped by page region. Designed for orientation — "what's on this page?" — without listing every element.
Everything in summary, plus all visible text content on the page.
Detail Levels
Level
Tokens
Use case
minimal
~50-200
Orientation after navigation. What regions exist? How many interactive elements?
summary
~500-5000
Working with the page. Full element list, form structures, content summaries.
full
variable
Reading page content. All visible text included.
Navigation tools default to minimal. The observe tool defaults to summary. Both accept an optional detail parameter to override.
Element IDs
Element IDs are stable across minor DOM mutations. They're generated by hashing a composite key of element type, ARIA role, accessible name, and DOM path signature:
v0.7.0 ID format change: element-ID hashes are now 6 hex characters (e.g. btn-a3f1c2), up from 4 in earlier releases. This drastically reduces cross-element hash collisions on large pages. Agents that hard-coded or pattern-matched 4-character IDs should re-find elements rather than reuse cached IDs across the upgrade.
IDs survive unrelated DOM changes and element reordering within the same container. When an agent navigates at minimal detail (no individual element IDs), it uses find to locate elements by text, type, or spatial proximity — the returned elements include IDs ready for interaction.
Development
# Run in watch mode
npm run dev
# Run all tests
npm test
# Run only unit tests
npm run test:unit
# Run only integration tests
npm run test:integration
# Type check
npx tsc --noEmit
Project Structure
src/
browser/ # Puppeteer lifecycle, tab management, CDP sessions
renderer/ # Accessibility tree extraction, layout, content, element IDs
state/ # Snapshot store, structural differ
tools/ # MCP tool definitions (navigation, observation, interaction, session, dev-mode)
dev/ # Static server, file watcher, auditor
types/ # TypeScript interfaces
utils/ # Logger, hash, wait utilities
tests/
unit/ # Fast tests with mocks
integration/ # Full Puppeteer tests against fixture HTML
fixtures/pages/ # Test HTML files
Architecture
The Renderer Pipeline is the core — it calls extractors in order and assembles a PageRepresentation:
Accessibility tree extraction (CDP Accessibility.getFullAXTree)
Layout extraction (CDP DOM.getBoxModel)
Landmark, heading, interactive element, and content extraction
Element ID generation (hash-based, stable across re-renders)
All tools go through renderActivePage() which handles snapshots, reload events, dialog detection, and response formatting.
Sandbox
Charlotte includes a test website in tests/sandbox/ that exercises all tools without touching the public internet. Serve it locally with:
dev_serve({ path: "tests/sandbox" })
Five pages cover navigation, forms, interactive elements, popups, delayed content, scroll containers, and more. See docs-internal/sandbox.md for the full page reference and a tool-by-tool exercise checklist.
Known Issues
Shadow DOM — Open shadow DOM works transparently. Chromium's accessibility tree pierces open shadow boundaries, so web components (e.g., GitHub's <relative-time>, <tool-tip>) render their content into Charlotte's representation without special handling. Closed shadow roots are opaque to the accessibility tree and will not be captured.
Roadmap
Session & Configuration
Feature Roadmap
Video Recording — Record interactions as video, capturing the full sequence of agent-driven navigation and manipulation for debugging, documentation, and review.
See docs-internal/playwright-mcp-gap-analysis.md for the full gap analysis against Playwright MCP, including lower-priority items (vision tools, testing/verification, tracing, transport, security) and areas where Charlotte has advantages.
Full Specification
See docs-internal/CHARLOTTE_SPEC.md for the complete specification including all tool parameters, the page representation format, element identity strategy, and architecture details.
