clipboard-mcp-server
by cyanheads
README.md
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<h1>@cyanheads/clipboard-mcp-server</h1>
<p><b>Read, write, and inspect the system clipboard across macOS, Linux (X11/Wayland), and Windows via MCP. STDIO or Streamable HTTP.</b>
<div>3 Tools</div>
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[](./CHANGELOG.md) [](./LICENSE) [](https://modelcontextprotocol.io/) [](https://www.npmjs.com/package/@cyanheads/clipboard-mcp-server) [](https://www.typescriptlang.org/) [](https://bun.sh/)
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[](https://github.com/cyanheads/clipboard-mcp-server/releases/latest/download/clipboard-mcp-server.mcpb) [](https://cursor.com/en/install-mcp?name=clipboard-mcp-server&config=eyJjb21tYW5kIjoibnB4IiwiYXJncyI6WyIteSIsIkBjeWFuaGVhZHMvY2xpcGJvYXJkLW1jcC1zZXJ2ZXIiXX0=) [](https://vscode.dev/redirect?url=vscode:mcp/install?%7B%22name%22%3A%22clipboard-mcp-server%22%2C%22command%22%3A%22npx%22%2C%22args%22%3A%5B%22-y%22%2C%22%40cyanheads%2Fclipboard-mcp-server%22%5D%7D)
[](https://www.npmjs.com/package/@cyanheads/mcp-ts-core)
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---
## Overview
The system clipboard across macOS, Linux (X11/Wayland), and Windows. Read, write, and inspect text, HTML, RTF, and image content from any MCP client. Runs as a stdio process or a local Streamable HTTP server.
### Tools
| Tool | Description |
|:---|:---|
| `clipboard_read` | Read clipboard contents in a specified format (text, HTML, RTF, image, or auto-select richest) |
| `clipboard_write` | Write plain text or HTML to the clipboard, replacing current contents, or clear it outright |
| `clipboard_inspect` | List available clipboard formats and byte sizes without reading full content |
---
## Capability reference
### `clipboard_read` <sub>tool</sub>
- `auto` returns the richest format explicitly present — priority: image > html > rtf > text — moving on to the next one when a listed format can't be read (an image no decoder accepts); `format` requests a specific one instead
- Size limits: 512 KB for text/HTML/RTF, 5 MB for images (raw bytes before base64 expansion)
- Content above the limit reads via `offset`/`limit` slicing — pass `offset` to read a bounded window (`limit` is optional, at least 4, and clamped to the format's size limit) and follow the returned `nextOffset` until `complete` is `true`
- Every read returns `representationId`, an opaque token for the value and format it was cut from — the same across full and sliced reads of an unchanged value. Pass it back with each `nextOffset`: if another application copied in between (even a same-size replacement), or `auto` now resolves to a different format, the continuation returns no bytes and fails with `representation_changed`. Linux and Windows derive it from a SHA-256 of the full representation, macOS from `NSPasteboard.changeCount`
- `image` returns base64-encoded PNG data, with `width`/`height` whenever the capture carries a readable PNG header. Only a response holding the whole image attaches an image block; image slices are PNG byte chunks, not standalone images — a partial slice carries its base64 and byte range in the text, and the chunks are base64-decoded separately and their bytes concatenated in offset order
- A text, HTML, RTF, or image format that is present but zero bytes long returns empty content, not an error (a zero-byte image attaches no image block)
- Typed errors: `format_unavailable` when the requested format isn't on the clipboard (or the clipboard is empty), `content_too_large` when no `offset`/`limit` was given and content exceeds the size limit, `representation_changed` when the clipboard changed after the slice that returned the given `representationId`, or while the read itself was running, `clipboard_unavailable` when the platform helper is missing or can't reach the desktop session, `inspect_unreadable` when `auto` can't read the clipboard's type listing (an explicit format reads without it)
---
### `clipboard_write` <sub>tool</sub>
- Exactly one of `content` or `clear: true` — an empty `content`, both, or neither is rejected as invalid input
- `format: "html"` writes HTML; macOS and Windows also publish an auto-generated, tag-stripped plain-text fallback. Linux has no stripped fallback — Wayland also offers the markup under the plain-text types, and X11 advertises only `text/html` but answers a plain-text request (e.g. `UTF8_STRING`) with the same markup, so a plain-text paste can receive raw HTML
- Typed `clipboard_unavailable` error when the platform helper is missing or can't reach the desktop session
- `clear: true` removes every representation instead of writing (needs `xsel` alongside `xclip` on Linux X11) and returns `cleared: true`, `byteSize: 0`, no `format`
- Returns `previousContent` — the plain text on the clipboard immediately before the write or clear, for undoing an unintended overwrite — absent when the clipboard was empty, held no text representation, or that text exceeded the 512 KB read limit
- Size limit: 1 MB, past which a typed `content_too_large` error is returned
- Not registered when `CLIPBOARD_READ_ONLY` is set, which gates clearing along with writing
---
### `clipboard_inspect` <sub>tool</sub>
- Returns `primaryFormat` (richest present — image > html > rtf > text — or `empty`) and `availableFormats` — only the formats `clipboard_read` can return, each backed by at least one representation that was read (the one exception: an image whose bytes no decoder accepts is listed, but reading it as `image` fails `format_unavailable`, and `auto` moves on to the next format)
- Returns `rawTypes` — every raw platform type identifier (UTIs on macOS, TARGETS on X11/Wayland, format names on Windows) with its measured `bytes`, where `0` means present and empty; a type the platform doesn't size (e.g. `TARGETS`) has no `bytes`, and one whose data was nil or unreadable carries `measurementFailed: true` and no `bytes` — never a false zero
- Typed `inspect_unreadable` error when the platform helper's output cannot be read, instead of reporting an empty clipboard; typed `clipboard_unavailable` when the helper is missing or can't reach the desktop session
---
## Features
Built on [`@cyanheads/mcp-ts-core`](https://github.com/cyanheads/mcp-ts-core): stdio and Streamable HTTP transports, pluggable auth (`none` / `jwt` / `oauth`), swappable storage (`in-memory`, `filesystem`, `Supabase`, `Cloudflare KV/R2/D1`), structured logging with optional OpenTelemetry tracing.
Clipboard-specific:
- Cross-platform backend detection at startup — macOS (osascript/JXA), Linux X11 (xclip), Linux Wayland (wl-clipboard), Windows (PowerShell 5.1+)
- Semantic format mapping — platform-native type identifiers (UTIs, TARGETS, Windows format names) mapped to `text`, `html`, `rtf`, `image` across all backends
- Platform-aware HTML writes — macOS and Windows publish HTML plus a stripped plain-text fallback; on Linux the HTML is the only payload, which plain-text paste targets can also receive
- Image support — every backend returns PNG as base64 with width/height (Linux backends read them from the PNG header)
Agent-friendly output:
- Size-guarded I/O — reads and writes over the format limit fail with a typed `content_too_large` error carrying byte/limit metadata, rather than truncating silently
- Bounded continuation — `clipboard_read` slices oversized content with `offset`/`limit` and `nextOffset` instead of forcing a single all-or-nothing read, and `representationId` makes a clipboard change between slices fail loudly instead of splicing two values together
- Undo support — `clipboard_write` returns `previousContent` so an unintended overwrite can be reverted
- Discriminated failure — `format_unavailable`, `content_too_large`, `representation_changed`, `inspect_unreadable`, and `clipboard_unavailable` are typed reasons with recovery hints, not generic errors; each backend classifies its helper's outcomes itself (across wl-clipboard and xclip release spellings), so an empty clipboard, an absent format, and an unreachable helper never blur together
---
## Getting started
Add the following to your MCP client configuration file.
```json
{
"mcpServers": {
"clipboard-mcp-server": {
"type": "stdio",
"command": "bunx",
"args": ["@cyanheads/clipboard-mcp-server@latest"],
"env": {
"MCP_TRANSPORT_TYPE": "stdio",
"MCP_LOG_LEVEL": "info"
}
}
}
}
```
Or with npx (no Bun required):
```json
{
"mcpServers": {
"clipboard-mcp-server": {
"type": "stdio",
"command": "npx",
"args": ["-y", "@cyanheads/clipboard-mcp-server@latest"],
"env": {
"MCP_TRANSPORT_TYPE": "stdio",
"MCP_LOG_LEVEL": "info"
}
}
}
}
```
For Streamable HTTP, set the transport and start the server:
```sh
MCP_TRANSPORT_TYPE=http MCP_HTTP_PORT=3010 bun run start:http
# Server listens at http://localhost:3010/mcp
```
### Prerequisites
Bun 1.4.0+ or Node.js 24+.
**macOS:** No additional tools required — `osascript` is built in.
**Linux X11:** `xclip` must be installed. `xsel` is additionally required for `clipboard_write`'s `clear` mode — it is the only one of the two that can hand the selection back rather than owning an empty one.
```sh
apt install xclip xsel # Debian/Ubuntu
pacman -S xclip xsel # Arch
```
**Linux Wayland:** `wl-clipboard` must be installed.
```sh
apt install wl-clipboard # Debian/Ubuntu
pacman -S wl-clipboard # Arch
```
**Windows:** PowerShell 5.1+ (built-in on Windows 10 and later).
---
## Configuration
| Variable | Description | Default |
|:---------|:------------|:--------|
| `MCP_TRANSPORT_TYPE` | Transport: `stdio` or `http`. | `stdio` |
| `MCP_HTTP_PORT` | Port for HTTP server. | `3010` |
| `MCP_HTTP_HOST` | Hostname for HTTP server. | `127.0.0.1` |
| `MCP_HTTP_ENDPOINT_PATH` | Endpoint path for the HTTP server. | `/mcp` |
| `MCP_HTTP_MAX_BODY_BYTES` | Max inbound JSON-RPC request body, in bytes. Raised above the framework's 1 MiB default so a full-size `clipboard_write` survives JSON escaping (worst case costs 6 wire bytes per source byte). `0` disables the guard and defers to the reverse proxy. | `7340032` |
| `MCP_SESSION_MODE` | HTTP session mode: `auto`, `stateful`, or `stateless`. `auto` resolves to `stateful`. This server defaults to `stateless` — it keeps no per-session state. | `stateless` |
| `MCP_AUTH_MODE` | Auth mode: `none`, `jwt`, or `oauth`. | `none` |
| `MCP_LOG_LEVEL` | Log level (`debug`, `info`, `notice`, `warning`, `error`). | `info` |
| `OTEL_ENABLED` | Enable [OpenTelemetry instrumentation](https://github.com/cyanheads/mcp-ts-core/tree/main/docs/telemetry). | `false` |
| `CLIPBOARD_READ_ONLY` | Serve the clipboard read-only. When `true`, `clipboard_write` is not registered — absent from `tools/list` and uncallable, though still shown in a disabled state on the manifest and landing page. Accepts `true/false/1/0/yes/no/on/off`; an unrecognized value fails startup. | `false` |
See [`.env.example`](./.env.example) for the full list of optional overrides.
---
## Running the server
### Local development
```sh
# One-time build
bun run rebuild
# Run the built server
bun run start:stdio
# or
bun run start:http
```
### Checks and tests
```sh
bun run devcheck # Lint, format, typecheck, security
bun run test # Vitest test suite
```
---
## Project structure
| Path | Purpose |
|:-----|:--------|
| `src/index.ts` | Entry point — registers tools via `createApp()` |
| `src/mcp-server/tools/definitions/` | Tool definitions: `clipboard_read`, `clipboard_write`, `clipboard_inspect` |
| `src/services/clipboard/` | Platform backends (macOS, Linux X11, Wayland, Windows) and service facade |
| `tests/` | Vitest tests for tools and backends |
| `framework-skills/` | Agent workflow skills (add-tool, field-test, polish-docs-meta, etc.) |
---
## Development guide
See [`CLAUDE.md`](./CLAUDE.md) for the full developer protocol — tool patterns, service patterns, error handling, logging conventions, and the checklist for shipping changes. The short version:
- Handlers throw, framework catches — tool logic catches only to act on a backend's typed outcome: map it to a declared error reason, or move `auto` on to the next format
- Use `ctx.log` for request-scoped logging
- No Docker — this server needs direct host OS access (JXA/NSPasteboard, xclip, wl-clipboard, PowerShell), none of which work inside a container
---
## Contributing
Issues welcome at [github.com/cyanheads/clipboard-mcp-server](https://github.com/cyanheads/clipboard-mcp-server). Run checks and tests before submitting:
```sh
bun run devcheck
bun run test
```
---
## License
Apache 2.0 — see [`LICENSE`](./LICENSE).
This server cannot be deployed
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