ModelContextProtocol: Fixing Specification Examples

by Alex Johnson 52 views

Hey everyone! Let's dive into a little heads-up regarding the ModelContextProtocol. It seems there's a small hiccup where the official examples provided don't quite line up with the actual specification defined in the schema.ts file. Specifically, we're talking about the title field within tool definitions. This might sound minor, but when we're building applications and relying on clear, consistent documentation, these discrepancies can cause a bit of confusion. Think of it like getting a recipe that lists an ingredient but then the actual cooking instructions leave it out – you're left wondering if you should use it or not! The good news is, this is a straightforward fix, and once corrected, it will make working with the protocol much smoother for everyone involved. We'll explore where this inconsistency lies and how the examples *should* look to perfectly match the specification.

Understanding the Discrepancy: Title vs. Annotations

Let's get specific about the ModelContextProtocol specification and where the examples seem to be taking a slight detour. When defining tools within the protocol, we often want to provide a human-readable name, or a title, that's more descriptive than just a technical name. The specification document, accessible at https://modelcontextprotocol.io/specification/2025-11-25/server/tools#listing-tools, shows an example tool definition like this:


{
        "name": "get_weather",
        "title": "Weather Information Provider",
        "description": "Get current weather information for a location",
        "inputSchema": {...}
}

This example clearly places the title field directly within the main object for the tool. It's intuitive; you have name, title, description, and then the schema. However, if we consult the actual TypeScript schema file, specifically at schema.ts, we find that the title field isn't defined at the top level of the tool object. Instead, the schema points towards the title being nested within an annotations object. Looking further down the schema.ts file, around line 1182, we see the structure for annotations, which is where metadata like titles are intended to reside.

This means the *correct* representation, aligning with the schema.ts definition, should actually look like this:


{
        "name": "get_weather",
        "description": "Get current weather information for a location",
        "inputSchema": {...},
        "annotations": {"title": "Weather Information Provider"}
}

You can see that the title has been moved inside the annotations object. This makes perfect sense from a schema design perspective, as annotations is often used as a container for supplementary, non-essential, or display-related metadata. The documentation found at /specification/2025-11-25/server/tools#tool also lists title as a direct property, which further compounds the confusion.

So, the core issue is this:

  • Official Example: Shows title as a top-level property.
  • schema.ts: Defines title within the annotations object.
  • Documentation: Lists title as a top-level property, mirroring the incorrect example.

This inconsistency can lead developers to implement tools using the example's structure, only to find that their implementations don't validate against the schema or function as expected. It's a classic case of the documentation and examples not quite keeping pace with the underlying technical definition. The fix involves updating both the examples and the documentation to reflect the actual schema structure. Let's explore why this matters and what the corrected versions would look like.

Why This Matters for Developers

The reason this seemingly small discrepancy in the ModelContextProtocol matters is quite significant for anyone developing applications that integrate with it. Developers rely heavily on specifications and examples to understand how to correctly use an API or protocol. When the provided examples deviate from the defined schema, it creates a breeding ground for errors and wasted effort. Imagine you're building a sophisticated AI agent that needs to call various tools, like fetching weather data. You'd look at the examples to see how to structure your tool calls.

If the example shows a `title` field at the top level, you'll likely include it there in your code. However, the actual `schema.ts` file, which is often the *source of truth* for validation, indicates that `title` belongs within `annotations`. This mismatch means:

  • Validation Failures: If you're using any form of schema validation (which is highly recommended!), your tool definitions might be rejected. The validator, adhering to `schema.ts`, won't recognize the `title` field in the top-level position.
  • Runtime Errors: Even if validation isn't strictly enforced, the system consuming these tool definitions might expect the `title` in the `annotations` object. This could lead to unexpected behavior or errors when the system tries to access the tool's metadata.
  • Confusion and Debugging Hell: Developers will spend valuable time debugging issues that stem from this inconsistency. They might initially blame their own code, only to discover later that the problem lies with the examples or documentation provided. This adds friction to the development process and can be incredibly frustrating.
  • Reduced Interoperability: A core goal of protocols like ModelContextProtocol is to ensure seamless interoperability between different systems. Consistent and accurate specifications are crucial for this. Inconsistencies can hinder the ability of various tools and platforms to work together harmoniously.

Furthermore, the documentation itself, which is meant to be a guiding light, is reinforcing the incorrect structure. The documentation states:

A tool definition includes:

* name: Unique identifier for the tool
* title: Optional human-readable name of the tool for display purposes.
* description: Human-readable description of functionality

This explicit mention of `title` as a direct property, alongside `name` and `description`, directly contradicts the `schema.ts` file. This makes it even harder for developers to spot the issue, as they're presented with conflicting information from multiple sources.

By correcting this, we ensure that:

  • Examples accurately reflect the schema.
  • Documentation aligns with both the examples and the schema.
  • Developers can confidently build integrations without encountering these specific types of validation or runtime issues.

It’s about maintaining the integrity and usability of the protocol, making it a more robust and developer-friendly standard.

The Corrected Specification and Examples

Let's lay out exactly how the ModelContextProtocol tool definitions should look, aligning perfectly with the schema.ts file. This involves adjusting both the example shown in the documentation and the way the documentation itself describes the tool structure. The key takeaway is that the title is not a direct property of the tool object but rather a property nested within the annotations object. This makes the main tool definition cleaner and reserves the top-level properties for essential functional aspects like name, description, and inputSchema, while metadata like titles are neatly tucked away.

Corrected Example Structure

Based on the schema.ts, the example for the `get_weather` tool should be presented as follows:


{
        "name": "get_weather",
        "description": "Get current weather information for a location",
        "inputSchema": {
          "type": "object",
          "properties": {
            "location": {
              "type": "string",
              "description": "The city and state, e.g. San Francisco, CA"
            }
          },
          "required": ["location"]
        },
        "annotations": {
            "title": "Weather Information Provider"
        }
}

Notice how the title field, previously at the root of the object, is now inside the annotations object. This structure is crucial for compatibility with any system that enforces the schema.ts. The annotations object acts as a designated place for optional, human-facing, or meta-information about the tool, keeping the core definition focused.

Corrected Documentation Snippet

Similarly, the documentation section describing a tool definition needs to be updated to reflect this nested structure. Instead of listing title as a direct property, it should be mentioned in the context of annotations.

A revised description could look something like this:

A tool definition includes:

*   name: Unique identifier for the tool (string).
*   description: Human-readable description of the tool's functionality (string).
*   inputSchema: The JSON schema defining the tool's input parameters.
*   annotations: An optional object containing additional metadata.
    *   title: An optional human-readable name of the tool for display purposes (string), nested within annotations.
    *   (Other potential annotation fields can also be defined here)

This revised documentation clearly indicates that title is part of the annotations object, removing the ambiguity. It also provides a more structured way to understand the properties, using code formatting for clarity.

The Rationale Behind Nesting

Why would the specification choose to nest the title within annotations? This design pattern is common in API and schema design for several good reasons:

  • Separation of Concerns: It clearly separates core functional properties (like name, description, inputSchema) from secondary, metadata-based properties (like title, icon, tags, etc.). This makes the schema easier to read, understand, and extend.
  • Extensibility: By using an annotations object, the protocol can easily introduce new metadata fields in the future without altering the core structure of the tool definition. Developers can add their own custom annotations as well.
  • Flexibility: Not all tools might need a human-readable title, or they might have other forms of descriptive metadata. Placing these under annotations makes them truly optional and doesn't clutter the main definition for tools that don't require them.
  • Tooling Compatibility: This structure is often favored by code generation tools and schema validation libraries, as it provides a predictable place for different types of information.

By ensuring that the examples and documentation accurately reflect this nested structure within annotations, the ModelContextProtocol becomes more consistent, predictable, and easier to work with for all developers.

Conclusion: Ensuring Consistency for a Smoother Developer Experience

In conclusion, the inconsistency between the official examples, documentation, and the schema.ts file for the ModelContextProtocol, specifically concerning the placement of the title field in tool definitions, is a critical point that needs addressing. While the examples and documentation currently suggest title is a top-level property, the actual schema dictates it should reside within the annotations object. This discrepancy can lead to significant confusion, validation errors, and debugging challenges for developers integrating with the protocol.

By rectifying this by updating the examples to correctly nest title within annotations and revising the documentation to accurately reflect this structure, we can ensure a much smoother and more predictable developer experience. This adherence to the schema not only prevents technical issues but also upholds the integrity and usability of the ModelContextProtocol as a standard. A consistent specification is the bedrock of good API design, fostering trust and encouraging wider adoption.

We strongly encourage the maintainers of the ModelContextProtocol to synchronize their examples and documentation with the definitive schema.ts file. This small but significant adjustment will undoubtedly benefit the entire community building on this protocol.

For further insights into API specifications and best practices, you can refer to resources like:

  • The OpenAPI Specification: OpenAPI Initiative - A widely adopted standard for describing RESTful APIs, which often employs similar concepts for metadata and schema definition.
  • JSON Schema: JSON Schema Organization - The standard for describing the structure of JSON data, crucial for understanding schema validation and best practices.