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DanielRamosAcosta

NixOS MCP Server

by DanielRamosAcosta
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TypeScript
Remote

NixOS MCP Server

A Model Context Protocol (MCP) server that enables searching NixOS configuration options directly from Claude Code.

Features

  • Search NixOS configuration options by keyword or phrase

  • Returns option names, types, default values, and descriptions

  • Pagination support for large result sets

  • Built with TypeScript and compatible with Node 24+

Related MCP server: mcp-nix

Requirements

  • Node.js 24 or later (for native TypeScript support)

  • npm or yarn

Installation

  1. Clone the repository:

cd /path/to/nixos-mcp
npm install

Configuration for Claude Code

To use this MCP server with Claude Code, you need to configure it in Claude Code's configuration file.

Linux/macOS

Edit ~/.config/claude/claude_code_config.json:

{
  "mcpServers": {
    "nixos-search": {
      "command": "node",
      "args": [
        "/absolute/path/to/nixos-mcp/src/index.ts"
      ]
    }
  }
}

Windows

Edit %APPDATA%\claude\claude_code_config.json:

{
  "mcpServers": {
    "nixos-search": {
      "command": "node",
      "args": [
        "C:\\absolute\\path\\to\\nixos-mcp\\src\\index.ts"
      ]
    }
  }
}

Restart Claude Code

After adding the configuration, restart Claude Code for the MCP server to be loaded.

Usage

Once configured, you can search NixOS options directly from Claude Code. Here are some example queries:

  • "Search for nginx options in NixOS"

  • "Find networking firewall configuration options"

  • "What NixOS options are available for SSH?"

  • "Search for services.postgresql options"

Available Tool

search_nixos_options

Searches NixOS configuration options.

Parameters:

  • query (string, required): Search query for NixOS options

    • Examples: "nginx", "networking firewall", "services.postgresql"

  • from (number, optional): Starting index for pagination

    • Default: 0

    • Use this to fetch subsequent pages of results

  • size (number, optional): Number of results per page

    • Default: 20

    • Range: 1-50

Example:

search_nixos_options {
  query: "nginx services",
  size: 10
}

Response Format:

Found X results for "query":

1. option.name.here
   Type: string
   Default: "default value"
   Description: Description of the option...

2. another.option.name
   Type: boolean
   Default: false
   Description: Another option description...

---
Showing results 1-10 of X total

Development

Run the Server Locally

To test the server without configuring Claude Code:

npm start

Code Quality

Format code:

npm run format

Type check:

npm run typecheck

Features

  • Efficient Search: Uses the official NixOS search API endpoint

  • NixOS 25.11: Searches against the latest NixOS channel (25.11)

  • Type-Safe: Full TypeScript type definitions

  • Validated Input: Zod schema validation for all inputs

  • Error Handling: Graceful error messages for invalid queries or API issues

  • Pagination Support: Handle large result sets efficiently

Architecture

src/
├── index.ts              # MCP server entry point
├── types.ts              # TypeScript type definitions
├── nixos-client.ts       # NixOS API client
└── tools/
    └── search-options.ts # Search tool implementation

Troubleshooting

Server won't start

  • Ensure you have Node 24 or later: node --version

  • Check that the path to src/index.ts is correct in the configuration

  • Look for error messages in Claude Code's MCP server logs

No results found

  • Try more specific search terms

  • Use common NixOS option names or prefixes (e.g., "services.nginx", "networking")

  • Check the NixOS search portal for reference

Connection issues

  • Make sure the config file syntax is valid JSON

  • Verify the absolute path is correct

  • Restart Claude Code after updating the configuration

API Details

This server uses the official NixOS search API:

  • Endpoint: https://search.nixos.org/backend/latest-44-nixos-25.11/_search

  • Channel: NixOS 25.11

  • Type: Only searches configuration options (not packages)

License

ISC

Available Tools

2 tools
search_nixos_optionsB

Search for NixOS configuration options by query. Returns matching options with their types, defaults, and descriptions.

ParametersJSON Schema
NameRequiredDescriptionDefault
queryYesSearch query for NixOS options (e.g., 'networking firewall', 'services nginx')
fromNoStarting index for pagination (default: 0)
sizeNoNumber of results to return (1-50, default: 20)

TDQS

B3.3/5.0
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 mentions the return format ('matching options with their types, defaults, and descriptions'), which is helpful, but doesn't cover important aspects like rate limits, authentication needs, error handling, or whether the search is case-sensitive. For a search tool with zero annotation coverage, this leaves significant gaps.

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, well-structured sentence that efficiently conveys the tool's purpose and return values. Every word earns its place, with no redundancy or unnecessary details. It's front-loaded with the core functionality.

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 moderate complexity (search with pagination), no annotations, and no output schema, the description is adequate but incomplete. It covers the basic purpose and return format, but lacks details on behavioral traits, usage context, and error handling. It meets minimum viability but has clear gaps.

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%, so the schema already documents all parameters thoroughly. The description adds no additional parameter semantics beyond what's in the schema—it doesn't explain query syntax, pagination behavior, or result ordering. Baseline 3 is appropriate when the schema does the heavy lifting.

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 ('Search for NixOS configuration options'), the resource ('NixOS configuration options'), and distinguishes from the sibling tool 'search_nix_packages' by specifying it's about configuration options rather than packages. It's precise and unambiguous.

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. While it implicitly suggests using it for searching NixOS options, there's no explicit mention of when not to use it or what other tools might be better for related tasks. It lacks context about prerequisites or typical use cases.

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

search_nix_packagesB

Search for Nix packages by query. Returns matching packages with their versions, descriptions, and maintainers.

ParametersJSON Schema
NameRequiredDescriptionDefault
queryYesSearch query for Nix packages (e.g., 'python', 'vim', 'firefox')
fromNoStarting index for pagination (default: 0)
sizeNoNumber of results to return (1-50, default: 20)

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. It mentions what the tool returns (packages with versions, descriptions, maintainers) but lacks important behavioral details like whether this is a read-only operation, if it requires authentication, rate limits, pagination behavior beyond the parameters, or error conditions. The description provides basic output information but misses key operational context.

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 extremely concise with just two sentences that efficiently convey the core functionality and return values. Every word earns its place with zero wasted text. The structure is front-loaded with the primary purpose followed by output details.

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?

For a search tool with 3 parameters, 100% schema coverage, but no annotations and no output schema, the description provides basic purpose and output information. However, it lacks important context about behavioral traits, error handling, and usage guidelines. The description is minimally adequate but has clear gaps in completeness given the tool's complexity and lack of supporting structured data.

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%, so the schema already fully documents all three parameters. The description doesn't add any parameter-specific information beyond what's in the schema. It mentions searching 'by query' which aligns with the 'query' parameter but doesn't provide additional semantic context. The baseline of 3 is appropriate when the schema does all the parameter documentation work.

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 tool's purpose: 'Search for Nix packages by query' with the verb 'search' and resource 'Nix packages'. It distinguishes from the sibling tool 'search_nixos_options' by specifying packages rather than options. However, it doesn't explicitly mention the sibling differentiation in the text itself.

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. There's no mention of the sibling tool 'search_nixos_options' or any other potential alternatives. The description simply states what the tool does without contextual usage information.

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

Tool Schema Changelog

Recent tool additions, removals, and schema changes observed during successful MCP inspections. Dates show when Glama detected each change.

  1. 2 tool updates
    • First observedsearch_nix_packages
    • First observedsearch_nixos_options
Install Server
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TDQS

B3.3/5.0
Disambiguation5/5

The two tools have clearly distinct purposes: one searches for NixOS configuration options, while the other searches for Nix packages. There is no overlap in functionality, and the descriptions explicitly differentiate between options (with types, defaults) and packages (with versions, maintainers).

Naming Consistency5/5

Both tools follow a consistent verb_noun pattern with 'search_' as the prefix, followed by the specific domain ('nixos_options' and 'nix_packages'). The naming is predictable and adheres to snake_case throughout, making it easy to understand the tool's purpose at a glance.

Tool Count2/5

With only two tools, the server feels thin for a domain as broad as NixOS/Nix package management. While the tools cover searching for options and packages, there are likely many other operations (e.g., installing packages, managing configurations) that are missing, making the toolset under-scoped for the apparent purpose.

Completeness2/5

The toolset is severely incomplete for a NixOS/Nix package management server. It only provides search functionality, with no tools for CRUD operations like installing packages, updating configurations, or managing system states. This creates significant gaps that will hinder agents from performing common workflows in this domain.

Maintenance

ActivityInactive
ResponsivenessSyncing

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