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 refactoring extracts common schema validation logic into a base Schema
class, eliminating ~100 lines of duplicate code between InputSchema and
OutputSchema. It also adds support for the JSON Schema `additionalProperties`
keyword to allow fine-grained control over extra properties in tool arguments.
Previously `additionalParameters` could be set only on OutputSchema.
Key changes:
- Created MCP::Tool::Schema base class consolidating:
- Schema validation against JSON Schema Draft 4 metaschema
- Deep key transformation (string to symbol conversion)
- $ref disallowance checking
- Common validation methods
- Refactored InputSchema to inherit from Schema:
- Simplified constructor to accept full schema hash
- Changed required fields storage from symbols to strings
- Removed ~40 lines of duplicated validation logic
- Refactored OutputSchema to inherit from Schema:
- Removed ~54 lines of duplicated validation logic
- Now shares all common functionality with InputSchema
- Updated Tool.input_schema setter:
- Simplified to pass full hash directly to InputSchema
- Added additionalProperties support:
- By default, tools now allow additional properties (JSON Schema default)
- Can explicitly set `additionalProperties: false` to disallow extras
- Added comprehensive test coverage for both behaviors
When starting an MCP server in Claude Code with `protocol_version` set to `DRAFT-2025-v3`,
it fails with the following error:
```console
2025-12-04T02:58:01.548Z [DEBUG] MCP server "example": Connection failed after 2093ms: Server's protocol version is not supported: DRAFT-2025-v3
2025-12-04T02:58:01.548Z [ERROR] MCP server "example" Connection failed: Server's protocol version is not supported: DRAFT-2025-v3
```
This PR changes the default behavior so that if `protocol_version` is not specified,
it uses the latest stable protocol version instead of the draft version.
This PR also updates the README to note that the latest stable protocol version includes
new features from the draft version.
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.
When defining a tool without any arguments taken, it should be allowed
to not have to define the `input_schema` at all, and the default value
for such a scenario should be `{ type: "object" }` as per the schema.
16d91abb68/schema/2025-06-18/schema.ts (L896-L900)
Currently, MCP has three versions: 2024-11-05, 2025-03-26, and 2025-06-18.
- https://modelcontextprotocol.io/specification/2024-11-05/basic/transports (stdio and HTTP with SSE)
- https://modelcontextprotocol.io/specification/2025-03-26/basic/transports (stdio and Streamable HTTP)
- https://modelcontextprotocol.io/specification/2025-06-18/basic/transports (stdio and Streamable HTTP)
The newer specification supports stdio and Streamable HTTP as transport mechanisms.
Only the oldest version, 2024-11-05, supports stdin and HTTP with SSE,
but that version is now considered legacy.
Given the current behavior of the Ruby SDK, it likely makes more sense to set
the default protocol version to the latest one, 2025-06-18, rather than the oldest, 2024-11-05.
Ideally, the implementation should adjust its behavior based on the version,
but this PR is limited to updating the default protocol version only.
## Motivation and Context
Currently, MCP supports the following three protocol versions:
"2025-06-18", "2025-03-26", and "2024-11-05".
https://modelcontextprotocol.io/introduction
As shown in the changes to `test/mcp/configuration_test.rb`,
the `protocol_version` value is not currently being validated,
which allows unexpected `protocol_version` values to be accepted.
This PR ensures that only supported protocol versions are accepted.
## How Has This Been Tested?
Existing tests have been updated and new tests have been added.
## Breaking Changes
None. If it becomes an issue, it means a value that was not originally intended has been used.
## Additional context
While one possible approach might be to fall back to a default protocol version
when an invalid `protocol_version` value is provided,
this PR opts to reject invalid `protocol_version` values explicitly.
The reasoning is that encouraging users to provide intentional,
valid input is preferable to silently falling back to a default,
which could lead to unexpected behavior.
- 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.
