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MCP Opener

by 3viky
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MCP Opener

Model Context Protocol server for opening files, folders, and browsers across different operating systems. Designed specifically to handle Linux Flatpak Firefox complexities on distributions like Fedora Bluefin.

Features

  • Open Folders: Launch system file manager (Nautilus, Finder, Explorer, etc.)

  • Open Files: Open files with their default applications

  • Open Browser: Open URLs with configurable browser preferences

  • Flatpak Firefox Support: Auto-detects and handles Flatpak Firefox installations

  • Cross-Platform: Works on Linux, macOS, and Windows

  • Smart File Handling: Automatically copies files to /tmp for Flatpak browser access when needed

Installation

# Install dependencies
pnpm install

# Build
pnpm build

# Install globally (optional)
pnpm link --global

Configuration

Configure via environment variables in your .env file or Claude Code MCP settings:

# Preferred browser: 'firefox' | 'chrome' | 'chromium' | 'default'
MCP_OPENER_BROWSER=firefox

# Explicitly set if Firefox is installed via Flatpak (auto-detected if omitted)
MCP_OPENER_FIREFOX_FLATPAK=true

# Whether to copy files to /tmp for Flatpak access (default: true)
MCP_OPENER_TMP_COPY=true

Claude Code Configuration

Add to your Claude Code MCP settings (.claude/settings.json or global settings):

{
  "mcpServers": {
    "opener": {
      "command": "node",
      "args": ["/path/to/mcp-opener/dist/index.js"],
      "env": {
        "MCP_OPENER_BROWSER": "firefox",
        "MCP_OPENER_FIREFOX_FLATPAK": "true",
        "MCP_OPENER_TMP_COPY": "true"
      }
    }
  }
}

Or using pnpm:

{
  "mcpServers": {
    "opener": {
      "command": "pnpm",
      "args": ["--dir", "/path/to/mcp-opener", "exec", "node", "dist/index.js"],
      "env": {
        "MCP_OPENER_BROWSER": "firefox"
      }
    }
  }
}

Tools

open_folder

Opens a folder in the system file manager.

Parameters:

  • path (string, required): Absolute or relative path to the folder

Example:

{
  "path": "/home/user/Documents"
}

Behavior by Platform:

  • Linux: Uses xdg-open, falls back to nautilus or dolphin

  • macOS: Uses open (Finder)

  • Windows: Uses explorer

open_file

Opens a file with its default application.

Parameters:

  • path (string, required): Absolute or relative path to the file

Example:

{
  "path": "./report.pdf"
}

Behavior by Platform:

  • Linux: Uses xdg-open

  • macOS: Uses open

  • Windows: Uses start

open_browser

Opens a URL in the preferred web browser.

Parameters:

  • url (string, required): URL to open (must start with http://, https://, or file://)

Example:

{
  "url": "https://github.com"
}

Behavior:

  1. Checks configured browser preference (MCP_OPENER_BROWSER)

  2. On Linux with Firefox:

    • Auto-detects Flatpak installation

    • For file:// URLs with Flatpak: Copies file to /tmp for accessibility

    • Uses flatpak run org.mozilla.firefox for Flatpak

    • Uses native firefox command otherwise

  3. Falls back to system default browser if preferred browser unavailable

Special Handling for Fedora Bluefin / Flatpak Firefox:

When opening local HTML files or other file:// URLs with Flatpak Firefox:

  1. File is copied to /tmp/mcp-opener-<random>/

  2. Browser opens the /tmp copy

  3. Cleanup happens after 5 seconds

This works around Flatpak's filesystem sandboxing restrictions.

Platform Support

Platform

File Manager

Browser Detection

Flatpak Support

Linux

xdg-open, Nautilus, Dolphin

✅

✅

macOS

Finder

✅

N/A

Windows

Explorer

✅

N/A

Usage Examples

From Claude Code

User: Open my Downloads folder
Agent: [Uses open_folder tool with path: /home/user/Downloads]

User: Open this README file
Agent: [Uses open_file tool with path: ./README.md]

User: Open GitHub in my browser
Agent: [Uses open_browser tool with url: https://github.com]

User: Preview this HTML file
Agent: [Uses open_browser tool with url: file:///home/user/project/index.html]
      [On Flatpak Firefox: Copies to /tmp, opens copy, cleans up]

Direct Tool Calls

// Open folder
{
  "name": "open_folder",
  "arguments": {
    "path": "/home/viky/Code"
  }
}

// Open file
{
  "name": "open_file",
  "arguments": {
    "path": "./package.json"
  }
}

// Open browser
{
  "name": "open_browser",
  "arguments": {
    "url": "https://anthropic.com"
  }
}

Error Handling

The server provides detailed error messages:

  • File/folder not found: "File does not exist: /path/to/file"

  • Invalid URL: "URL must start with http://, https://, or file://"

  • Platform not supported: "Unsupported platform: <platform>"

  • No file manager found: "No file manager found (tried xdg-open, nautilus, dolphin)"

Development

# Watch mode for development
pnpm dev

# Build for production
pnpm build

# Test the server manually
echo '{"method":"tools/list"}' | node dist/index.js

Troubleshooting

Flatpak Firefox not detected

Check if Firefox is installed via Flatpak:

flatpak list --app | grep firefox

If installed, you should see org.mozilla.firefox. Set MCP_OPENER_FIREFOX_FLATPAK=true explicitly if auto-detection fails.

Files not opening in Flatpak Firefox

Ensure MCP_OPENER_TMP_COPY=true (default). The server will copy files to /tmp for Flatpak accessibility.

Wrong browser opens

Set MCP_OPENER_BROWSER explicitly:

MCP_OPENER_BROWSER=firefox
# or
MCP_OPENER_BROWSER=chrome
# or
MCP_OPENER_BROWSER=default

License

MIT

Author

3viky

Contributing

Issues and PRs welcome at github.com/3viky/mcp-opener

Available Tools

3 tools
open_browserA

Open a URL in the preferred web browser. Supports Firefox (including Flatpak), Chrome, and system default.

ParametersJSON Schema
NameRequiredDescriptionDefault
urlYesURL to open (must start with http://, https://, or file://)

TDQS

A3.7/5.0
Behavior3/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

With no annotations provided, the description carries the full burden of behavioral disclosure. It adds useful context about supported browsers and URL protocol requirements (implied by the schema), but it does not cover aspects like error handling, platform dependencies, or what happens if the browser is not installed. The description provides some behavioral insight but leaves gaps for a mutation tool.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is appropriately sized and front-loaded, consisting of a single, efficient sentence that directly states the tool's function and supported browsers without unnecessary details. Every part of the sentence earns its place by providing essential information, making it highly concise and well-structured.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness3/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given the tool's complexity (simple mutation with one parameter), no annotations, and no output schema, the description is moderately complete. It covers the basic action and browser support but lacks details on behavioral traits like error responses or system requirements. For a tool with no annotations, it should do more to fully inform the agent, resulting in an adequate but incomplete description.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

The schema description coverage is 100%, with the parameter 'url' fully documented in the schema (including protocol requirements). The description does not add any additional meaning or semantics beyond what the schema provides, such as examples or edge cases. Given the high schema coverage, the baseline score of 3 is appropriate as the description does not compensate or enhance parameter understanding.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states the specific action ('Open a URL') and resource ('in the preferred web browser'), distinguishing it from sibling tools like open_file and open_folder which handle different resources. It provides explicit detail about supported browsers (Firefox, Chrome, system default), making the purpose unambiguous and distinct.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines3/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description implies usage by specifying supported browsers, but it does not explicitly state when to use this tool versus alternatives like open_file or open_folder. It provides some context (browser types) but lacks guidance on exclusions or direct comparisons with sibling tools, leaving the agent to infer appropriate usage scenarios.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

open_fileB

Open a file with its default application

ParametersJSON Schema
NameRequiredDescriptionDefault
pathYesAbsolute or relative path to the file to open

TDQS

B3.1/5.0
Behavior2/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

No annotations are provided, so the description carries the full burden of behavioral disclosure. It states the tool opens a file with its default application, implying a system-level action that may launch external apps, but doesn't mention potential side effects like requiring specific permissions, handling errors, or system dependencies. For a tool with zero annotation coverage, this leaves significant gaps in understanding its behavior.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is a single, efficient sentence that directly states the tool's function without unnecessary words. It is front-loaded with the core action and resource, making it easy to understand quickly. Every part of the sentence contributes to clarity, with no wasted information.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness3/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given the tool's low complexity (one parameter, no output schema, no annotations), the description is minimally adequate. It covers the basic action but lacks details on behavioral aspects like error handling or system requirements. Without annotations or output schema, it should provide more context for safe use, but it meets the bare minimum for a simple tool.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, with the single parameter 'path' documented in the schema as 'Absolute or relative path to the file to open'. The description adds no additional meaning beyond this, such as examples or constraints. Since the schema does the heavy lifting, the baseline score of 3 is appropriate, as the description doesn't compensate but also doesn't detract.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose4/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states the action ('Open') and resource ('a file'), specifying it opens with the default application. It distinguishes from sibling tools like 'open_browser' and 'open_folder' by focusing specifically on files, though it doesn't explicitly contrast them. The purpose is unambiguous but could be more specific about sibling differentiation.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines2/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description provides no guidance on when to use this tool versus alternatives like 'open_browser' or 'open_folder'. It lacks context about scenarios where opening a file is appropriate compared to opening a browser or folder, and offers no prerequisites or exclusions. Usage is implied by the action but not explicitly defined.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

open_folderA

Open a folder in the system file manager (Nautilus, Finder, Explorer, etc.)

ParametersJSON Schema
NameRequiredDescriptionDefault
pathYesAbsolute or relative path to the folder to open

TDQS

A3.5/5.0
Behavior2/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

No annotations are provided, so the description carries the full burden of behavioral disclosure. It states the action ('Open a folder') but does not describe what happens upon execution (e.g., whether it launches an application, requires user permissions, handles errors, or has side effects). This leaves significant gaps in understanding the tool's behavior beyond the basic action.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is a single, efficient sentence that front-loads the core action and resource, with no wasted words. It is appropriately sized for the tool's simplicity, making it easy to parse and understand quickly.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness3/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given the tool's low complexity (one parameter, no output schema, no annotations), the description is minimally adequate. It covers the purpose and basic usage but lacks details on behavioral traits, error handling, or integration with the system, which could be helpful for an agent to invoke it correctly in varied contexts.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

The input schema has 100% description coverage, with the 'path' parameter fully documented. The description does not add any meaning beyond what the schema provides (e.g., no examples of path formats or constraints), so it meets the baseline of 3 for high schema coverage without compensating with extra details.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states the specific action ('Open a folder') and resource ('in the system file manager'), with explicit examples (Nautilus, Finder, Explorer) that distinguish it from sibling tools like open_browser and open_file. It provides a complete, unambiguous purpose statement.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines3/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description implies usage by specifying the tool opens folders in file managers, but it does not explicitly state when to use this tool versus alternatives like open_file or open_browser. No guidance on prerequisites, exclusions, or specific contexts is provided, leaving usage somewhat open to interpretation.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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TDQS

A3.8/5.0
Disambiguation5/5

Each tool has a clearly distinct purpose: open_browser for URLs, open_file for files, and open_folder for directories. There is no overlap in functionality, making it easy for an agent to select the correct tool based on the target type.

Naming Consistency5/5

All tool names follow a consistent verb_noun pattern (open_browser, open_file, open_folder) with the same verb 'open' and descriptive nouns. This uniformity enhances readability and predictability.

Tool Count5/5

With 3 tools, the server is well-scoped for its purpose of opening resources (URLs, files, folders). Each tool earns its place by covering a distinct aspect of the domain without redundancy or bloat.

Completeness5/5

The tool surface is complete for the domain of opening resources, covering URLs, files, and folders. There are no obvious gaps, as these three categories encompass the typical use cases for an opener utility.

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