fcp-plugins

File Context Protocol (FCP)

MCP servers that let LLMs interact with complex file formats through a verb-based DSL.

FCP is to MCP what React is to the DOM — the LLM thinks in domain operations, FCP renders them into the target format.

Installation

FCP is a Claude Code marketplace plugin. Add it to your settings.json:

{
  "marketplace_plugins": {
    "fcp@os-tack/fcp": true
  }
}

This installs all FCP servers automatically. Prerequisites by server:

Server	Requires
fcp-drawio	Node.js
fcp-midi	Python 3.13+
fcp-terraform	Go
fcp-rust	rust-analyzer
fcp-sheets	Python 3.13+
fcp-slides	Python 3.13+

Manual Installation (non-Claude Code)

Each server can be installed and configured independently. Add to your MCP client config:

{
  "mcpServers": {
    "fcp-drawio": {
      "command": "npx",
      "args": ["-y", "@os-tack/fcp-drawio"]
    },
    "fcp-terraform": {
      "command": "fcp-terraform"
    }
  }
}

See each server's README for full installation instructions: fcp-drawio · fcp-midi · fcp-terraform · fcp-rust · fcp-sheets · fcp-slides

Quick Start

Here's a complete workflow — create a diagram from scratch, inspect it, and save:

> drawio_session("new \"Auth Flow\"")

! session "Auth Flow" created
[0s 0e 0g p:1/1]

> drawio(["add svc AuthService theme:blue", "add db UserDB theme:green", "connect AuthService -> UserDB label:\"queries\" style:dashed"])

+ svc AuthService @(0,0 140x60) blue
+ db UserDB @(200,0 120x80) green
~ AuthService -> UserDB "queries" dashed
[2s 1e 0g 320x80 p:1/1]

> drawio_query("status")

status: "Auth Flow" (unsaved, 4 ops, 0 checkpoints)
  page: Page 1 (2 shapes, 1 edge, 0 groups)

> drawio_session("save as:./auth-flow.drawio")

! saved ./auth-flow.drawio
[2s 1e 0g 320x80 p:1/1]

Every FCP server follows this same pattern: session → mutations → query → save.

Servers

Server	Format	Description
fcp-drawio	draw.io diagrams	Architecture diagrams, flowcharts, ERDs
fcp-midi	MIDI music	Notes, chords, tracks, instruments
fcp-terraform	Terraform HCL	AWS/GCP/Azure infrastructure
fcp-rust	Rust codebases	Navigation, inspection, refactoring via rust-analyzer
fcp-sheets	Excel spreadsheets	Tables, formulas, charts, formatting
fcp-slides	PowerPoint presentations	Slides, shapes, tables, charts, layouts

What the LLM Sees

Every mutation returns a prefixed response and a digest line summarizing the current state. This gives the LLM structured feedback without reading the whole file:

Prefix	Meaning
+	Created
~	Modified / connected
*	Style / metadata changed
-	Removed
!	Meta operation
@	Bulk / layout

Examples

Diagrams — shapes, edges, and a bounding-box digest:

> drawio(["add svc API theme:blue", "connect API -> DB"])

+ svc API @(0,0 140x60) blue
~ API -> DB
[2s 1e 0g 320x80 p:1/1]

Music — notes, chords, and a song-state digest:

> midi(["note Piano C4 at:1.1 dur:quarter vel:mf", "chord Strings Am at:2.1 dur:whole"])

+ note C4 at:1.1 dur:quarter vel:mf
+ chord Am at:2.1 dur:whole
[1t 4e tempo:120 4/4 2bars]

Infrastructure — resources, variables, and a block-count digest:

> terraform(["add resource aws_instance web ami:\"ami-0c55b159\" instance_type:t2.micro", "add variable region default:\"us-east-1\""])

+ resource aws_instance.web ami:"ami-0c55b159" instance_type:t2.micro
+ variable region default:"us-east-1"
2 blocks, 1 resource, 1 variable

Rust — symbol navigation, diagnostics, and refactoring:

> rust_session("open /path/to/my-project")

! session opened: /path/to/my-project (42 .rs files)

> rust_query("find Config @kind:struct")

Config (struct) src/config.rs:12
  fields: name, port, database_url

> rust(["rename old_handler handle_request @file:routes.rs"])

~ renamed old_handler → handle_request (3 references updated)

Spreadsheets — data blocks and a sheet-state digest:

> sheets(["data A1", "Name,Age,City", "Alice,30,NYC", "Bob,25,LA", "data end"])

+ Wrote 3 rows at A1
1 sheets, ~6 cells

Presentations — slides, shapes, and a deck-state digest:

> slides(["slide add layout:title", "placeholder set title \"Q4 Review\"", "placeholder set subtitle \"Finance Team\""])