## Summary
Unlike applications, libraries provide value by remaining usable for a broad range of users,
even when that means supporting older Ruby versions beyond Ruby's own EOL timeline.
I maintain RuboCop, a Ruby linter. Because linters need to work across the ecosystem,
they often need to keep compatibility with older Ruby versions to some extent.
The trade-off is that the MCP Ruby SDK must remain compatible with Ruby 2.7.
However, given the ecosystem impact, supporting Ruby 2.7 is still worthwhile.
For example, bundled gems such as `csv` (Ruby >= 2.5), `bigdecimal` (Ruby >= 2.5), `json` (Ruby >= 2.7),
and `language_server-protocol` (Ruby >= 2.5) tend to keep compatibility with older Ruby versions.
Unlike dropping support, which imposes restrictions on users,
this change broadens compatibility and does not introduce breaking changes.
## Development Note
`rubocop-shopify` (2.18) supports Ruby 3.1+, and this PR does not change that.
Since RuboCop can configure the runtime Ruby version and the target Ruby version for analysis independently,
CI continues to run RuboCop on Ruby 4.0, while analyzing code with `TargetRubyVersion: 2.7`.
When setting `TargetRubyVersion: 2.7`, several RuboCop offenses were resolved.
Additionally, Sorbet-related libraries support Ruby 3.0+. Since these are not dependencies of the MCP Ruby SDK itself,
they are versioned and tested in the development Gemfile.
Claude Code sometimes only shows `Error: MCP error -32603: Internal error`
when an unexpected exception occurs during a tool call.
This change broadens the exception handling scope so the server can surface
the exception message more often, making failures easier to diagnose.
This raises an exception when duplicate tool names are registered,
instead of silently overwriting tools. Tool names are required to be
unique within a server, so this behavior aligns with the MCP specification.
> Tool names SHOULD be unique within a server.
https://modelcontextprotocol.io/specification/2025-11-25/server/tools#tool-names
Validation for tool names could be made more strictly spec-compliant in a separate effort.
Fixes#197
This PR adds support for the optional `websiteUrl` parameter in `serverInfo`.
This parameter has been supported since the 2025-11-25 MCP specification.
This PR also implements part of https://github.com/modelcontextprotocol/ruby-sdk/issues/127.
Consolidates four identical constructions of error `Tool::Response` in
`handle_call_tool_request` into a single private `error_tool_response` method,
reducing duplication and improving maintainability. No behavior change.
For example, the `title` introduced in #109 is not supported in the latest stable protocol version "2025-06-18":
https://modelcontextprotocol.io/specification/2025-06-18
It is supported in the Draft of the next version:
https://modelcontextprotocol.io/specification/draft
In other words, the fact that the Ruby SDK treats "2025-06-18" as the default protocol version while `title` is
only supported in the Draft results in an inconsistency.
Because of this, a new version `"Draft"` has been added to the list of supported versions.
Its value follows the schema below and is defined as `DRAFT-2025-v3`:
14ec41c/schema/draft/schema.ts (L15)
It was also considered to continue using the latest stable version "2025-06-18" as the Ruby SDK default instead of the Draft.
However, in that case, users would need to explicitly specify `MCP::Server.new(protocol_version: 'DRAFT-2025-v3')`,
which adds extra burden. In this PR, Draft is made the default in order to provide the following benefits:
- Users are likely to prefer using the Draft version over the latest stable version
- No need to specify the `protocol_version` option when initializing `MCP::Server`
- Users generally do not need to know the internal development value `DRAFT-2025-v3`
The primary case for specifying `protocol_version` explicitly is when strict adherence to a particular version is required.
However, it seems more practical to prioritize use cases where backward-compatible features, including those from the Draft,
are desirable. This is the rationale behind making the Draft version the default.
In addition, making the Draft version the default protocol version preserves backward compatibility for `MCP::Server`.
NOTE: `DRAFT-2025-v3` is a development code, so its value cannot be set externally.
It is applied either when `protocol_version` is omitted or when `nil` is set explicitly,
such as with `MCP::Configuration.new(protocol_version: nil)`.
This prevents users from creating implementations that depend on development codes like `DRAFT-2025-v3`.
Tool execution errors now return successful responses with isError: true
instead of JSON-RPC protocol errors, per the MCP specification.
This allows clients to distinguish between protocol-level errors and
tool execution errors, providing better error context.
Fixes#159
* Add support for _meta field on tool schema
* use `meta` naming for `_meta` field on tool schema
* apply suggestions to fix `_meta` tests
Co-authored-by: Ateş Göral <ates@magnetiq.com>
* Update lib/mcp/tool.rb
Co-authored-by: Ateş Göral <ates@magnetiq.com>
* Update lib/mcp/tool.rb
Co-authored-by: Ateş Göral <ates@magnetiq.com>
---------
Co-authored-by: Topher Bullock <topherbullock@users.noreply.github.com>
Co-authored-by: Ateş Göral <ates@magnetiq.com>
There are some unused block variables. This change removes block parameters
that consist solely of unused block parameters.
Where `Hash#values` suffices instead of ignoring unused variables,
replace such code with `Hash#values`.
Since the optional `title` becomes `title: null` when not provided, the following error occurs.
This occurs with Claude Code 1.0.100.
```console
[DEBUG] MCP server "example": Connection failed after 1591ms: [
{
"code": "invalid_type",
"expected": "string",
"received": "null",
"path": [
"serverInfo",
"title"
],
"message": "Expected string, received null"
}
]
```
By adding `compact`, the `title` key will be removed if the optional `title` keyword argument is not specified.
`handle_request` already adds the `method` to the instrumentation data,
so there is no need to repeat this. Moreover, consumers can override
these anyway.
- Updated `call` method in `MCP::Tool` and `MCP::Prompt` to accept `server_context` as an optional parameter.
- Refactored `MCP::Server` to streamline argument handling for tool and prompt calls, introducing helper methods `call_tool_with_args` and `call_prompt_template_with_args`.
- Adjusted tests to reflect changes in method signatures and ensure compatibility with optional `server_context` parameter.
Refactor capabilities handling into MCP::Server::Capabilities to improve
code organization and separation of concerns. This provides a cleaner API
for configuring server capabilities including prompts, resources, tools,
completions, logging, and experimental features.
🤖 Generated with [Claude Code](https://claude.ai/code)
Co-Authored-By: Claude <noreply@anthropic.com>
