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CHANGELOG.md

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Server JSON Schema Changelog

Changes to the server.json schema and format.

Draft (Unreleased)

This section tracks changes that are in development and not yet released. The draft schema is available at server.schema.json in this repository.

Changed

  • No changes yet.

Notes

When ready for release, changes in this section will be moved to a dated version section (e.g., ## 2025-XX-XX) and the schema will be published to a versioned URL.

2025-12-11

Changed

URL Template Variables for Remote Servers (#570)

Remote servers can now define URL template variables using {curly_braces} notation. This enables multi-tenant deployments where a single server definition can support multiple endpoints with configurable values.

Example:

{
  "remotes": [{
    "type": "streamable-http",
    "url": "https://{tenant_id}.api.example.com/mcp",
    "variables": {
      "tenant_id": {
        "description": "Your tenant identifier",
        "isRequired": true
      }
    }
  }]
}

Migration: No changes required. Existing servers continue to work unchanged.

2025-10-17

Changed

The version field is now optional for MCPB packages, providing flexibility for publishers.

Key Changes:

  • MCPB packages can now include an optional version field - Previously rejected by validation, MCPB packages can now optionally specify a version field for clarity and metadata purposes.
  • Both formats are valid:
    • MCPB packages with version field: Provides explicit version metadata
    • MCPB packages without version field: Version information is embedded in the download URL (as before)

Migration:

Publishers using MCPB packages can optionally add a version field to their package configuration. This is particularly useful when:

  • The version information is not clearly visible in the download URL
  • You want to provide explicit version metadata for tooling and clients
  • You need consistent version tracking across different package types

Existing MCPB packages without the version field continue to work without any changes.

Example - MCPB Package with optional version:

{
  "packages": [{
    "registryType": "mcpb",
    "identifier": "https://github.com/example/releases/download/v1.0.0/package.mcpb",
    "version": "1.0.0",
    "fileSha256": "fe333e598595000ae021bd27117db32ec69af6987f507ba7a63c90638ff633ce",
    "transport": {
      "type": "stdio"
    }
  }]
}

Example - MCPB Package without version (still valid):

{
  "packages": [{
    "registryType": "mcpb",
    "identifier": "https://github.com/example/releases/download/v1.0.0/package.mcpb",
    "fileSha256": "fe333e598595000ae021bd27117db32ec69af6987f507ba7a63c90638ff633ce",
    "transport": {
      "type": "stdio"
    }
  }]
}

Schema Version

  • Schema version: 2025-10-11 → 2025-10-17

2025-10-11

Changed

Package Format Enhancements (#634)

The Package schema has been refactored to better support different package types with dedicated handling per registry type.

Key Changes:

  • version field is now optional - Previously required for all packages, now only used by npm, pypi, and nuget. OCI packages include version in the identifier (e.g., ghcr.io/owner/repo:v1.0.0), and MCPB packages use direct download URLs.

  • Enhanced documentation - Added detailed comments explaining which fields are relevant for each registryType:

    • NPM/PyPI/NuGet: Use registryType, identifier (package name), version, optional registryBaseUrl
    • OCI: Use registryType, identifier (full image reference with tag)
    • MCPB: Use registryType, identifier (download URL), fileSha256 (required)

  • Field clarifications:

    • identifier: Now clearly documented as package name for registries, full image reference for OCI, or download URL for MCPB
    • fileSha256: Clarified as required for MCPB packages and optional for other types
    • registryBaseUrl: Clarified as used by npm/pypi/nuget but not by oci/mcpb

Migration:

Publishers using OCI or MCPB packages can now omit the version field, as it's either embedded in the identifier (OCI) or not applicable (MCPB direct downloads). Publishers using npm, pypi, or nuget should continue to provide the version field as before.

Example - OCI Package (version in identifier):

{
  "packages": [{
    "registryType": "oci",
    "identifier": "ghcr.io/modelcontextprotocol/server-example:v1.2.3",
    "transport": {
      "type": "stdio"
    }
  }]
}

Example - MCPB Package (no version field):

{
  "packages": [{
    "registryType": "mcpb",
    "identifier": "https://github.com/example/releases/download/v1.0.0/package.mcpb",
    "fileSha256": "fe333e598595000ae021bd27117db32ec69af6987f507ba7a63c90638ff633ce",
    "transport": {
      "type": "stdio"
    }
  }]
}

Schema Version

  • Schema version: 2025-09-29 → 2025-10-11

2025-09-29

⚠️ BREAKING CHANGES

Schema Simplification

Removed registry-managed fields from publisher-controlled server.json schema.

Removed fields:

  • status field from Server object (now managed by registry in API responses)
  • io.modelcontextprotocol.registry/official from _meta (read-only, added by registry)

Migration: Publishers should remove these fields from their server.json files. The registry will manage server status and official metadata separately.

Changed

  • Schema version: 2025-09-16 → 2025-09-29

2025-09-16

⚠️ BREAKING CHANGES

Field Names: snake_case → camelCase (#428)

All JSON field names standardized to camelCase. All existing server.json files must be updated.

Changed fields:

  • registry_type → registryType
  • registry_base_url → registryBaseUrl
  • file_sha256 → fileSha256
  • runtime_hint → runtimeHint
  • runtime_arguments → runtimeArguments
  • package_arguments → packageArguments
  • environment_variables → environmentVariables
  • is_required → isRequired
  • is_secret → isSecret
  • value_hint → valueHint
  • is_repeated → isRepeated
  • website_url → websiteUrl

Migration Examples

Package Configuration:

// OLD - Will be rejected
{
  "packages": [{
    "registry_type": "npm",
    "registry_base_url": "https://registry.npmjs.org",
    "file_sha256": "abc123...",
    "runtime_hint": "node",
    "runtime_arguments": [...],
    "package_arguments": [...],
    "environment_variables": [...]
  }]
}

// NEW - Required format
{
  "packages": [{
    "registryType": "npm",
    "registryBaseUrl": "https://registry.npmjs.org",
    "fileSha256": "abc123...",
    "runtimeHint": "node",
    "runtimeArguments": [...],
    "packageArguments": [...],
    "environmentVariables": [...]
  }]
}

Arguments Configuration:

// OLD - Will be rejected
{
  "runtime_arguments": [
    {
      "name": "port",
      "is_required": true,
      "is_repeated": false,
      "value_hint": "8080"
    }
  ]
}

// NEW - Required format
{
  "runtimeArguments": [
    {
      "name": "port",
      "isRequired": true,
      "isRepeated": false,
      "valueHint": "8080"
    }
  ]
}

Environment Variables:

// OLD - Will be rejected
{
  "environment_variables": [
    {
      "name": "API_KEY",
      "is_required": true,
      "is_secret": true
    }
  ]
}

// NEW - Required format
{
  "environmentVariables": [
    {
      "name": "API_KEY",
      "isRequired": true,
      "isSecret": true
    }
  ]
}

Migration Checklist for Publishers

  • Update your server.json files to use camelCase field names
  • Test server publishing with new CLI version
  • Update any automation scripts that reference old field names
  • Update documentation referencing old field names

Updated Schema Reference

🔗 Current schema: https://static.modelcontextprotocol.io/schemas/2025-09-29/server.schema.json

Changed

  • Schema version: 2025-07-09 → 2025-09-16

2025-07-09

Initial release of the server.json schema.