80cb03ff7a<!-- Provide a brief summary of your changes --> ## Motivation and Context <!-- Why is this change needed? What problem does it solve? --> This resolves https://github.com/modelcontextprotocol/registry/issues/738. There are two issues with the NuGet.org integration today: 1. Change the `registryBaseUrl` for NuGet to `https://api.nuget.org/v3/index.json`. `https://api.nuget.org` is not the entry point for our service and is not specific enough. `https://api.nuget.org/v3/index.json` is the value that users put into their tooling to connect to our public registry (it is installed by default in .NET client tooling). 2. Use the service index API to get the URL pattern for package READMEs. - This URL is not guaranteed to be stable. The service index URL (`registryBaseUrl`) is, however. Additionally, I polished up the error messages so various error modes are clearer. When packages are published to NuGet.org, they take 2-5 minutes to become available due to validations we run. Some possible states that are now handled and described more helpfully are: - Version exists, but the package has no README - The ID exists, but the version does not - The ID does not exist at all There are only 3 authors (me, another MSFT person, and a community member) explicitly setting the old value. The DB migration will fix the issue. A future publish will fail with the validation error but the error message is clear. `registry type and base URL do not match: 'https://api.nuget.org' is not valid for registry type 'nuget'. Expected: https://api.nuget.org/v3/index.json` ## How Has This Been Tested? <!-- Have you tested this in a real application? Which scenarios were tested? --> - Unit tests, new and existing - Manual test locally - Set old data in the DB, `docker compose up`, confirm the migration updates the specific package ## Breaking Changes Yes, but minimal impact expected, unless there is a dependency on the specific `https://api.nuget.org` value downstream. I am not aware of any such dependency, and the new value is more proper and specific. ## Types of changes <!-- What types of changes does your code introduce? Put an `x` in all the boxes that apply: --> - [ ] Bug fix (non-breaking change which fixes an issue) - [x] New feature (non-breaking change which adds functionality) - [x] Breaking change (fix or feature that would cause existing functionality to change) - [x] Documentation update ## Checklist <!-- Go over all the following points, and put an `x` in all the boxes that apply. --> - [x] I have read the [MCP Documentation](https://modelcontextprotocol.io) - [x] My code follows the repository's style guidelines - [x] New and existing tests pass locally - [x] I have added appropriate error handling - [x] I have added or updated documentation as needed ## Additional context <!-- Add any other context, implementation notes, or design decisions --> For more information about the NuGet API see: https://learn.microsoft.com/en-us/nuget/api/overview#service-index (I wrote most of the docs).
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server.json Format Specification
A server.json file is a standardized way to describe MCP servers for registry publishing, client discovery, and package management.
Also see:
- For step-by-step instructions on creating and using server.json files, see the publishing guide.
- For understanding the validation requirements when publishing to the official registry, see official registry requirements.
Browse the Complete Schema
📋 View the full specification interactively: Open server.schema.json in a schema viewer like json-schema.app.
The schema contains all field definitions, validation rules, examples, and detailed descriptions.
The official registry has some more restrictions on top of this. See the official registry requirements for details.
Extension Metadata with _meta
The optional _meta field allows publishers to include custom metadata alongside their server definitions using reverse DNS namespacing.
{
"_meta": {
"io.modelcontextprotocol.registry/publisher-provided": {
// Your custom metadata here
}
}
}
When publishing to the official registry, custom metadata must be placed under the key io.modelcontextprotocol.registry/publisher-provided. See the official registry requirements for detailed restrictions and examples.
Examples
Basic Server with NPM Package
{
"$schema": "https://static.modelcontextprotocol.io/schemas/2025-10-17/server.schema.json",
"name": "io.modelcontextprotocol.anonymous/brave-search",
"description": "MCP server for Brave Search API integration",
"title": "Brave Search",
"websiteUrl": "https://anonymous.modelcontextprotocol.io/examples",
"repository": {
"url": "https://github.com/modelcontextprotocol/servers",
"source": "github"
},
"version": "1.0.2",
"packages": [
{
"registryType": "npm",
"registryBaseUrl": "https://registry.npmjs.org",
"identifier": "@modelcontextprotocol/server-brave-search",
"version": "1.0.2",
"transport": {
"type": "stdio"
},
"environmentVariables": [
{
"name": "BRAVE_API_KEY",
"description": "Brave Search API Key",
"isRequired": true,
"isSecret": true
}
]
}
],
"_meta": {
"io.modelcontextprotocol.registry/publisher-provided": {
"tool": "npm-publisher",
"version": "1.0.1",
"build_info": {
"timestamp": "2023-12-01T10:30:00Z"
}
}
}
}
Server in a Monorepo with Subfolder
For MCP servers located within a subdirectory of a larger repository (monorepo structure), use the subfolder field to specify the relative path:
{
"$schema": "https://static.modelcontextprotocol.io/schemas/2025-10-17/server.schema.json",
"name": "io.modelcontextprotocol/everything",
"description": "MCP server that exercises all the features of the MCP protocol",
"title": "Everything",
"repository": {
"url": "https://github.com/modelcontextprotocol/servers",
"source": "github",
"subfolder": "src/everything"
},
"version": "0.6.2",
"packages": [
{
"registryType": "npm",
"registryBaseUrl": "https://registry.npmjs.org",
"identifier": "@modelcontextprotocol/everything",
"version": "0.6.2",
"transport": {
"type": "stdio"
}
}
],
"_meta": {
"io.modelcontextprotocol.registry/publisher-provided": {
"tool": "npm-publisher",
"version": "1.0.1",
"build_info": {
"timestamp": "2023-12-01T10:30:00Z"
}
}
}
}
Constant (fixed) arguments needed to start the MCP server
Suppose your MCP server application requires a mcp start CLI arguments to start in MCP server mode. Express these as positional arguments like this:
{
"$schema": "https://static.modelcontextprotocol.io/schemas/2025-10-17/server.schema.json",
"name": "io.github.joelverhagen/knapcode-samplemcpserver",
"description": "Sample NuGet MCP server for a random number and random weather",
"version": "0.4.0-beta",
"packages": [
{
"registryType": "nuget",
"registryBaseUrl": "https://api.nuget.org/v3/index.json",
"identifier": "Knapcode.SampleMcpServer",
"version": "0.4.0-beta",
"transport": {
"type": "stdio"
},
"packageArguments": [
{
"type": "positional",
"value": "mcp"
},
{
"type": "positional",
"value": "start"
}
]
}
],
"_meta": {
"io.modelcontextprotocol.registry/publisher-provided": {
"tool": "nuget-publisher",
"version": "2.1.0",
"build_info": {
"timestamp": "2023-11-15T14:22:00Z",
"pipeline_id": "nuget-build-456"
}
}
}
}
This will essentially instruct the MCP client to execute dnx Knapcode.SampleMcpServer@0.4.0-beta -- mcp start instead of the default dnx Knapcode.SampleMcpServer@0.4.0-beta (when no packageArguments are provided).
Filesystem Server with Multiple Packages
{
"$schema": "https://static.modelcontextprotocol.io/schemas/2025-10-17/server.schema.json",
"name": "io.github.modelcontextprotocol/filesystem",
"description": "Node.js server implementing Model Context Protocol (MCP) for filesystem operations.",
"title": "Filesystem",
"repository": {
"url": "https://github.com/modelcontextprotocol/servers",
"source": "github",
"id": "b94b5f7e-c7c6-d760-2c78-a5e9b8a5b8c9"
},
"version": "1.0.2",
"packages": [
{
"registryType": "npm",
"registryBaseUrl": "https://registry.npmjs.org",
"identifier": "@modelcontextprotocol/server-filesystem",
"version": "1.0.2",
"transport": {
"type": "stdio"
},
"packageArguments": [
{
"type": "positional",
"valueHint": "target_dir",
"description": "Path to access",
"default": "/Users/username/Desktop",
"isRequired": true,
"isRepeated": true
}
],
"environmentVariables": [
{
"name": "LOG_LEVEL",
"description": "Logging level (debug, info, warn, error)",
"default": "info"
}
]
},
{
"registryType": "oci",
"identifier": "docker.io/mcp/filesystem:1.0.2",
"transport": {
"type": "stdio"
},
"runtimeArguments": [
{
"type": "named",
"description": "Mount a volume into the container",
"name": "--mount",
"value": "type=bind,src={source_path},dst={target_path}",
"isRequired": true,
"isRepeated": true,
"variables": {
"source_path": {
"description": "Source path on host",
"format": "filepath",
"isRequired": true
},
"target_path": {
"description": "Path to mount in the container. It should be rooted in `/project` directory.",
"isRequired": true,
"default": "/project"
}
}
}
],
"packageArguments": [
{
"type": "positional",
"valueHint": "target_dir",
"value": "/project"
}
],
"environmentVariables": [
{
"name": "LOG_LEVEL",
"description": "Logging level (debug, info, warn, error)",
"default": "info"
}
]
}
],
"_meta": {
"io.modelcontextprotocol.registry/publisher-provided": {
"tool": "ci-publisher",
"version": "3.2.1",
"build_info": {
"commit": "a1b2c3d4e5f6789",
"timestamp": "2023-12-01T10:30:00Z",
"pipeline_id": "filesystem-build-789",
"environment": "production"
}
}
}
}
Remote Server Example
{
"$schema": "https://static.modelcontextprotocol.io/schemas/2025-10-17/server.schema.json",
"name": "io.modelcontextprotocol.anonymous/mcp-fs",
"description": "Cloud-hosted MCP filesystem server",
"repository": {
"url": "https://github.com/example/remote-fs",
"source": "github",
"id": "xyz789ab-cdef-0123-4567-890ghijklmno"
},
"version": "2.0.0",
"remotes": [
{
"type": "streamable-http",
"url": "https://mcp-fs.anonymous.modelcontextprotocol.io/http"
}
],
"_meta": {
"io.modelcontextprotocol.registry/publisher-provided": {
"tool": "cloud-deployer",
"version": "2.4.0",
"build_info": {
"commit": "f7e8d9c2b1a0",
"timestamp": "2023-12-05T08:45:00Z",
"deployment_id": "remote-fs-deploy-456",
"region": "us-west-2"
}
}
}
}
Python Package Example
{
"$schema": "https://static.modelcontextprotocol.io/schemas/2025-10-17/server.schema.json",
"name": "io.github.example/weather-mcp",
"description": "Python MCP server for weather data access",
"title": "Weather",
"repository": {
"url": "https://github.com/example/weather-mcp",
"source": "github",
"id": "def456gh-ijkl-7890-mnop-qrstuvwxyz12"
},
"version": "0.5.0",
"packages": [
{
"registryType": "pypi",
"registryBaseUrl": "https://pypi.org",
"identifier": "weather-mcp-server",
"version": "0.5.0",
"runtimeHint": "uvx",
"transport": {
"type": "stdio"
},
"environmentVariables": [
{
"name": "WEATHER_API_KEY",
"description": "API key for weather service",
"isRequired": true,
"isSecret": true
},
{
"name": "WEATHER_UNITS",
"description": "Temperature units (celsius, fahrenheit)",
"default": "celsius"
}
]
}
],
"_meta": {
"io.modelcontextprotocol.registry/publisher-provided": {
"tool": "poetry-publisher",
"version": "1.8.3",
"build_info": {
"python_version": "3.11.5",
"timestamp": "2023-11-28T16:20:00Z",
"build_id": "pypi-weather-123",
"dependencies_hash": "sha256:a9b8c7d6e5f4"
}
}
}
}
NuGet (.NET) Package Example
The dnx tool ships with the .NET 10 SDK, starting with Preview 6.
{
"$schema": "https://static.modelcontextprotocol.io/schemas/2025-10-17/server.schema.json",
"name": "io.github.joelverhagen/knapcode-samplemcpserver",
"description": "Sample NuGet MCP server for a random number and random weather",
"repository": {
"url": "https://github.com/joelverhagen/Knapcode.SampleMcpServer",
"source": "github",
"id": "example-nuget-id-0000-1111-222222222222"
},
"version": "0.5.0",
"packages": [
{
"registryType": "nuget",
"registryBaseUrl": "https://api.nuget.org/v3/index.json",
"identifier": "Knapcode.SampleMcpServer",
"version": "0.5.0",
"runtimeHint": "dnx",
"transport": {
"type": "stdio"
},
"environmentVariables": [
{
"name": "WEATHER_CHOICES",
"description": "Comma separated list of weather descriptions to randomly select.",
"isRequired": true,
"isSecret": false
}
]
}
],
"_meta": {
"io.modelcontextprotocol.registry/publisher-provided": {
"tool": "dotnet-publisher",
"version": "8.0.100",
"build_info": {
"dotnet_version": "8.0.0",
"timestamp": "2023-12-10T12:15:00Z",
"configuration": "Release",
"target_framework": "net8.0",
"build_number": "20231210.1"
}
}
}
}
Complex Docker Server with Multiple Arguments
{
"$schema": "https://static.modelcontextprotocol.io/schemas/2025-10-17/server.schema.json",
"name": "io.github.example/database-manager",
"description": "MCP server for database operations with support for multiple database types",
"repository": {
"url": "https://github.com/example/database-manager-mcp",
"source": "github",
"id": "ghi789jk-lmno-1234-pqrs-tuvwxyz56789"
},
"version": "3.1.0",
"packages": [
{
"registryType": "oci",
"identifier": "docker.io/example/database-manager-mcp:3.1.0",
"transport": {
"type": "stdio"
},
"runtimeArguments": [
{
"type": "named",
"name": "--network",
"value": "host",
"description": "Use host network mode"
},
{
"type": "named",
"name": "-e",
"value": "DB_TYPE={db_type}",
"description": "Database type to connect to",
"isRepeated": true,
"variables": {
"db_type": {
"description": "Type of database",
"choices": [
"postgres",
"mysql",
"mongodb",
"redis"
],
"isRequired": true
}
}
}
],
"packageArguments": [
{
"type": "named",
"name": "--host",
"description": "Database host",
"default": "localhost",
"isRequired": true
},
{
"type": "named",
"name": "--port",
"description": "Database port",
"format": "number"
},
{
"type": "positional",
"valueHint": "database_name",
"description": "Name of the database to connect to",
"isRequired": true
}
],
"environmentVariables": [
{
"name": "DB_USERNAME",
"description": "Database username",
"isRequired": true
},
{
"name": "DB_PASSWORD",
"description": "Database password",
"isRequired": true,
"isSecret": true
},
{
"name": "SSL_MODE",
"description": "SSL connection mode",
"default": "prefer",
"choices": [
"disable",
"prefer",
"require"
]
}
]
}
],
"_meta": {
"io.modelcontextprotocol.registry/publisher-provided": {
"tool": "docker-buildx",
"version": "0.12.1",
"build_info": {
"docker_version": "24.0.7",
"timestamp": "2023-12-08T14:30:00Z",
"platform": "linux/amd64,linux/arm64",
"registry": "docker.io",
"image_digest": "sha256:1a2b3c4d5e6f7890"
}
}
}
}
Server with Remote and Package Options
{
"$schema": "https://static.modelcontextprotocol.io/schemas/2025-10-17/server.schema.json",
"name": "io.modelcontextprotocol.anonymous/hybrid-mcp",
"description": "MCP server available as both local package and remote service",
"title": "Hybrid",
"repository": {
"url": "https://github.com/example/hybrid-mcp",
"source": "github",
"id": "klm012no-pqrs-3456-tuvw-xyz789abcdef"
},
"version": "1.5.0",
"packages": [
{
"registryType": "npm",
"registryBaseUrl": "https://registry.npmjs.org",
"identifier": "@example/hybrid-mcp-server",
"version": "1.5.0",
"runtimeHint": "npx",
"transport": {
"type": "stdio"
},
"packageArguments": [
{
"type": "named",
"name": "--mode",
"description": "Operation mode",
"default": "local",
"choices": [
"local",
"cached",
"proxy"
]
}
]
}
],
"remotes": [
{
"type": "streamable-http",
"url": "https://mcp.anonymous.modelcontextprotocol.io/http",
"headers": [
{
"name": "X-API-Key",
"description": "API key for authentication",
"isRequired": true,
"isSecret": true
},
{
"name": "X-Region",
"description": "Service region",
"default": "us-east-1",
"choices": [
"us-east-1",
"eu-west-1",
"ap-southeast-1"
]
}
]
},
{
"type": "sse",
"url": "https://mcp.anonymous.modelcontextprotocol.io/sse"
}
],
"_meta": {
"io.modelcontextprotocol.registry/publisher-provided": {
"tool": "hybrid-deployer",
"version": "1.7.2",
"build_info": {
"timestamp": "2023-12-03T11:00:00Z",
"deployment_strategy": "blue-green",
"npm_version": "10.2.4",
"node_version": "20.10.0",
"service_endpoints": {
"sse": "deployed",
"streamable": "deployed"
}
}
}
}
}
MCP Bundle (MCPB) Package Example
{
"$schema": "https://static.modelcontextprotocol.io/schemas/2025-10-17/server.schema.json",
"name": "io.modelcontextprotocol/text-editor",
"description": "MCP Bundle server for advanced text editing capabilities",
"title": "Text Editor",
"repository": {
"url": "https://github.com/modelcontextprotocol/text-editor-mcpb",
"source": "github"
},
"version": "1.0.2",
"packages": [
{
"registryType": "mcpb",
"identifier": "https://github.com/modelcontextprotocol/text-editor-mcpb/releases/download/v1.0.2/text-editor.mcpb",
"fileSha256": "fe333e598595000ae021bd27117db32ec69af6987f507ba7a63c90638ff633ce",
"transport": {
"type": "stdio"
}
}
],
"_meta": {
"io.modelcontextprotocol.registry/publisher-provided": {
"tool": "mcpb-publisher",
"version": "1.0.0",
"build_info": {
"timestamp": "2023-12-02T09:15:00Z",
"bundle_format": "mcpb-v1"
}
}
}
}
This example shows an MCPB (MCP Bundle) package that:
- Is hosted on GitHub Releases (an allowlisted provider)
- Includes a SHA-256 hash for integrity verification
- Can be downloaded and executed directly by MCP clients that support MCPB
Embedded MCP inside a CLI tool
Some CLI tools bundle an MCP server, without a standalone MCP package or a public repository. In these cases, reuse the existing packages shape by pointing at the host CLI package and supplying the packageArguments and runtimeHint if needed to start the MCP server.
{
"$schema": "https://static.modelcontextprotocol.io/schemas/2025-10-17/server.schema.json",
"name": "io.snyk/cli-mcp",
"description": "MCP server provided by the Snyk CLI",
"title": "Snyk",
"version": "1.1298.0",
"packages": [
{
"registryType": "npm",
"registryBaseUrl": "https://registry.npmjs.org",
"identifier": "snyk",
"version": "1.1298.0",
"transport": {
"type": "stdio"
},
"packageArguments": [
{ "type": "positional", "value": "mcp" },
{
"type": "named",
"name": "-t",
"description": "Transport type for MCP server",
"default": "stdio",
"choices": ["stdio", "sse"]
}
]
}
]
}
Server with Custom Installation Path
For MCP servers that follow a custom installation path or are embedded in applications without standalone packages, use the websiteUrl field to direct users to setup documentation:
{
"$schema": "https://static.modelcontextprotocol.io/schemas/2025-10-17/server.schema.json",
"name": "io.modelcontextprotocol.anonymous/embedded-mcp",
"description": "MCP server embedded in a Desktop app",
"websiteUrl": "https://anonymous.modelcontextprotocol.io/embedded-mcp-guide",
"version": "0.1.0"
}