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Relax outputSchema to any JSON Schema 2020-12 document per SEP-2106 (#1568)

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Co-authored-by: Mike Kistler <mikekistler@microsoft.com>
This commit is contained in:
Jayaraman Venkatesan 2026-06-16 18:02:04 -04:00 • committed by GitHub
commit 0663b7c878
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1 changed files with 839 additions and 260 deletions
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23
src/ModelContextProtocol.Core/Protocol/Tool.cs
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@ -81,17 +81,24 @@ public sealed class Tool : IBaseMetadata
} = McpJsonUtilities.DefaultMcpToolSchema;
/// <summary>
/// Gets or sets a JSON Schema object defining the expected structured outputs for the tool.
/// Gets or sets a JSON Schema document describing the shape of the tool's structured output.
/// </summary>
/// <exception cref="ArgumentException">The value is not a valid MCP tool JSON schema.</exception>
/// <exception cref="ArgumentException">
/// The value is not a valid JSON Schema 2020-12 document — i.e., not a JSON object or a
/// JSON boolean.
/// </exception>
/// <remarks>
/// <para>
/// The schema must be a valid JSON Schema object with the "type" property set to "object".
/// This is enforced by validation in the setter which will throw an <see cref="ArgumentException"/>
/// if an invalid schema is provided.
/// Per SEP-2106 ("Allow valid JSON Schemas in <c>outputSchema</c>"), the schema may describe
/// any JSON value — object, array, string, number, boolean, or <see langword="null"/> — to
/// support tools whose structured output is not an object. The setter only checks that the
/// supplied value is a structurally valid JSON Schema 2020-12 document (a JSON object, or
/// the boolean schemas <c>true</c>/<c>false</c> per §4.3); deeper keyword-level validation
/// is intentionally not performed.
/// </para>
/// <para>
/// The schema should describe the shape of the data as returned in <see cref="CallToolResult.StructuredContent"/>.
/// The schema describes the shape of the value placed in <see cref="CallToolResult.StructuredContent"/>.
/// Unlike <see cref="InputSchema"/>, the top-level <c>type</c> is not required to be <c>"object"</c>.
/// </para>
/// </remarks>
[JsonPropertyName("outputSchema")]
@ -100,9 +107,9 @@ public sealed class Tool : IBaseMetadata
get => field;
set
{
if (value is not null && !McpJsonUtilities.IsValidMcpToolSchema(value.Value))
if (value is not null && !McpJsonUtilities.IsValidToolOutputSchema(value.Value))
{
throw new ArgumentException("The specified document is not a valid MCP tool output JSON schema.", nameof(OutputSchema));
throw new ArgumentException("The specified document is not a valid JSON Schema 2020-12 document (must be a JSON object or a JSON boolean).", nameof(OutputSchema));
}
field = value;