Limner MCP Server

Limner: A Harnessed Image-generation Agent

A Harnessed Image-generation Agent: Claude reasons, Cloudflare executes, D1 remembers, OAuth is the only way in.

Limner is an Agent Harness and Model Context Protocol (MCP) server for orchestrating image generation across multiple pipelines, with durable memory for project context. This repository is rasa, the foundation variant of the Limner family. You deploy rasa as your own instance: free as in beer, no strings or data pipelines attached.

Contents

• The Harnessed Agent
• Decisions and dead-ends
• Architecture
• Stack
• Tool Surface
• Memory
• Security
• Prerequisites
• Quickstart
• Testing and feedback
• Roadmap
• The Limner family
• Contributing
• License
• Acknowledgments

The Harnessed Agent

Limner is explicitly built as a composable harness with clean seams:

• The reasoning loop runs on Anthropic's Claude Managed Agents platform. The model does the planning and the tool choice. It never holds provider credentials and never executes code.
• Tool execution runs in Cloudflare V8 isolates. Every tool call lands in a Worker: deterministic TypeScript with explicit bindings, not a shell. Image composition happens in-isolate (WASM codecs, raster ops, text rendering) so the common path costs nothing and leaks nothing.
• The seam between them is an OAuth-gated MCP surface. The agent reaches the tools the same way any MCP client does: dynamic client registration, a bearer token, and a typed tool contract at /mcp. There is no private side channel.
• Memory is a database, not a context window. Project briefs, style decisions, and progress notes live in D1 and survive across sessions. The agent recalls what it recorded last week instead of being re-told.

The same tool surface ships three ways from one codebase: the OAuth-gated Workers endpoint, a local stdio server, and a .mcpb one-click bundle for Claude Desktop. The stdio server identifies itself as limner-mcp (preview): stdio is the preview transport at v1, pending a refresh against the next MCP spec revision. The Workers and .mcpb surfaces carry no preview tag.

Decisions and dead-ends

The design did not arrive fully formed. The full record lives in docs/Limner_Cloudflare_CMA_Architecture.md: 22 dated decision records, a cost model, and five named off-ramp triggers that state in advance what would make us walk away from the approach.

Several of those records are reversals. The FastAPI shim that fronted the first design was killed. The Sharp/libvips composition path was abandoned for a hybrid WASM stack that runs inside the isolate. Recraft began as a composed first-party MCP and was later amended to a direct REST call, with the transport seam kept as a reusable adapter. One record is a correction: a request timed out at 30s during integration testing and was first blamed on an upstream API, until the API's own docs turned up an async mode and the fault turned out to be ours.

The "Deploy to Cloudflare" button is the cleanest dead-end (currently). We ran the spike on 2026-06-12. The button's monorepo mode extracts a single package into a standalone repo, which severs the @limner/core workspace dependency and breaks the build. Provisioning and secrets worked; the repo shape did not. The full note, and the script that does the same job plus migrations and a smoke test, is under Where is the Deploy to Cloudflare button?.

Architecture

Stack

• TypeScript pnpm monorepo: @limner/core (pipelines, composition, state), @limner/mcp (the server, all three transports), @limner/cma-tools (the same tool contract packaged for CMA custom-tool consumption)
• Cloudflare Workers, D1, KV, R2, Durable Objects, Images
• Composition: Photon and jSquash (WASM), Satori + resvg for typography, Cloudflare Images for the network-side ops
• MCP over Streamable HTTP and stdio

The architecture document with decision records lives at docs/Limner_Cloudflare_CMA_Architecture.md.

Tool Surface

All tools are namespaced limner_*. Full schemas in packages/limner-mcp/README.md.

Memory

Most image tools start every session from zero. Limner records what a project is and what you decided, then reads it back on the next run. Two stores back this, both in D1 (or local SQLite for the stdio and .mcpb flavors):

• Categorized memory. limner_record writes a fact under a category with an idempotent upsert, so re-recording the same key updates in place instead of piling up duplicates. limner_recall reads a category back, limner_forget removes an entry, and limner_list_categories enumerates what exists. Use it for durable preferences: a house palette, a default aspect ratio, a model that works for a given look.
• Project context. limner_create_project opens a project, limner_record_project_note appends running notes (briefs, style decisions, progress), limner_get_project_context returns the brief and notes for a project, and limner_list_projects lists them. This is the "what were we doing last week" layer.

Nothing here is a vector database or an embedding model. It is plain structured state with explicit keys, which is the point: the agent recalls what it actually recorded, not the nearest fuzzy match.

Security

A few properties hold by construction, worth stating for anyone running their own instance:

• One way in. The Workers endpoint is OAuth 2.1 with dynamic client registration and PKCE. First authorization shows a consent screen with a double-submit CSRF token (a __Host- cookie plus a signed hidden field); the issued scope is pinned, and deny paths validate the redirect URI against registration before redirecting.
• Artifacts are signed and expiring. Generated images are served from R2 behind HMAC-signed capability URLs with a short TTL, verified in constant time. On a public origin, delivery fails closed if the signing key is unset. SVG is served with content-type pinning and a sandbox policy; raster is served inline.
• Outbound fetches are guarded. Every fetch the server makes on your behalf (reference images, provider calls) runs through an SSRF guard that blocks loopback, link-local, unique-local, and metadata ranges, and re-resolves hostnames to catch rebinding.
• The common path leaks nothing. In-isolate composition needs no network and no credentials; only the generation tools and the five cf* ops reach outside the isolate, and only with the provider key you supplied.

Prerequisites

For a self-deployed Workers stack:

• A Cloudflare account with Workers, D1, and KV available (the free plan covers all three, including SQLite Durable Objects)
• R2 enabled on the account (free tier; the artifact bucket is created for you)
• A Cloudflare Images paid plan for the five cf* compose ops at real usage volumes
• An OpenAI API key and a Recraft API key. Both are required up front; the generation tools spend your own provider credit
• Node per .nvmrc (22; floor 22.13) and pnpm 10

A note on the Images free tier: Cloudflare includes 5,000 unique transformations per month on every account, after which the cf* ops return errors until the month rolls over. That allowance is fine for kicking the tires; treat the paid plan as the requirement for actual use. The eleven in-isolate compose ops never touch Images and stay free everywhere.

Local stdio and .mcpb need no Cloudflare account at all: state goes to local SQLite, and the cf* compose ops refuse cleanly.

Quickstart

Pick the heaviest option you have patience for. They all end at the same tool surface.

Provisioning script

git clone https://github.com/vinsonconsulting/limner.git
cd limner
pnpm install --frozen-lockfile
pnpm setup:cloudflare

The script checks your wrangler login, provisions D1, KV, and R2 by name (re-running is safe), pins the resource ids into the wrangler config, applies the schema migration, builds, deploys, prompts for both provider keys, smoke-tests the deployed endpoint, and prints connect instructions for Claude Desktop, Claude Code, and MCP Inspector.

Optional: pnpm setup:cloudflare --with-example-seed loads a small generic memory seed (a fictional postcard project) so the memory tools have something to recall on day one. --env production provisions the separate production environment, and --dry-run shows the plan without changing anything.

Where is the Deploy to Cloudflare button?

Sigh... we tried, in a live spike (2026-06-12). The button's monorepo mode extracts packages/limner-mcp into a standalone repository, which severs the @limner/core workspace dependency, so the build cannot succeed regardless of build settings. Its provisioning and secrets flow worked well; the repo shape is the blocker. The script above does everything the button would, plus migrations and a smoke test. If the button gains in-place monorepo support, it returns here.

For push-to-deploy CI/CD in the meantime, connect your fork through the dashboard: Workers and Pages, import the repository, root directory /, build command pnpm install --frozen-lockfile && pnpm -r build, deploy command pnpm --filter @limner/mcp run deploy. That flow keeps the full repository, so the workspace resolves.

Manual

The script above is a convenience wrapper over five wrangler commands; the by-hand version is in the comments of packages/limner-mcp/wrangler.toml. Short form: wrangler d1 create limner-rasa-dev, wrangler kv namespace create OAUTH_KV, wrangler r2 bucket create limner-rasa-artifacts-dev, pin the printed ids in the config, then wrangler d1 migrations apply limner-rasa-dev --remote, wrangler secret put both keys, and wrangler deploy.

Local stdio (no Cloudflare account)

git clone https://github.com/vinsonconsulting/limner.git
cd limner
pnpm install --frozen-lockfile
pnpm -r build
OPENAI_API_KEY=sk-... RECRAFT_API_KEY=... node packages/limner-mcp/dist/stdio.js

For Claude Desktop, add to ~/Library/Application Support/Claude/claude_desktop_config.json:

{
  "mcpServers": {
    "limner": {
      "command": "node",
      "args": ["/absolute/path/to/limner/packages/limner-mcp/dist/stdio.js"],
      "env": { "OPENAI_API_KEY": "sk-...", "RECRAFT_API_KEY": "..." }
    }
  }
}

.mcpb bundle (Claude Desktop one-click)

Download the .mcpb from a GitHub release (built on mcpb-v* tags), open it with Claude Desktop, and fill in the API-key prompts. Or build your own: pnpm pack:mcpb.

Connecting a client to a deployed Worker

claude mcp add --transport http limner https://limner-mcp.<your-subdomain>.workers.dev/mcp

Claude Desktop: Settings, Connectors, add a custom connector with the same URL. MCP Inspector: npx @modelcontextprotocol/inspector, then connect with the Streamable HTTP transport. OAuth dynamic client registration handles credentials in all three cases.

Testing and feedback

docs/TESTING.md is the tester's checklist, ordered free-first and paid-last, with the cost of every step stated up front. Findings are public issues: use the test finding or bug report template.

Roadmap

Near-term, in rough order:

• MCP spec refresh (2026-07-28). Move the transports to the stateless model the new revision defines and drop the per-session id. This is what promotes stdio out of preview; the Workers and .mcpb surfaces are already current.
• Token-footprint instrumentation. Measure real per-turn token cost and round-trip counts in live traffic before pulling any schema-reduction lever, so the decision is driven by numbers rather than guesses.
• More MCP clients. Keep validating rasa against additional MCP hosts and conformance harnesses, and fold the findings back into the tool contract.
• The family. limner-pixel (pixel art) and limner-ascii (ASCII workflows) build on rasa; see The Limner family.

The Limner family

Limner is a family of model harnesses. Each variant builds on rasa (this repo) and adds opinions for a specific creative niche.

Specialty pipelines (pixel-art generators like Pixellab and RetroDiffusion) are being built in limner-pixel (not yet public); rasa stays general-purpose. The legacy proprietary work that preceded the OSS pivot is kept private at vinsonconsulting/limner-pixel-legacy.

Contributing

Contributions welcome. See CONTRIBUTING.md. All commits need a Developer Certificate of Origin sign-off via git commit -s; the DCO check gates merge.

License

Apache-2.0 © Jim Vinson · jimvinson.com

Acknowledgments

Limner is built on Anthropic's Claude Managed Agents platform and Cloudflare's CMA hosting. Limner is an independent project; "built on" does not imply endorsement by Anthropic or Cloudflare.

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