Changelog

All notable changes to the MCP Description Specification are documented here. The format is based on Keep a Changelog. The specification uses versioning aligned with its mcpdesc field.

[0.7.0] — 2026-03-23

Changed

Simplified tags to flat structure — removed hierarchical nesting. The Tag Object no longer includes a recursive tags property. All tags are now declared in a flat array at the root level.
Tag uniqueness requirement simplified — tag names MUST be unique across all tags (previously “across the entire tag tree”).
Tag reference validation simplified — per-entity tags must reference tag names declared in the root tags array (no nesting levels to traverse).
Added uniqueItems: true constraint to per-entity tags arrays on tools, resources, resource templates, and prompts to prevent duplicate tag references.

Removed

Removed hierarchical tag support — Tag Objects no longer support nested tags arrays. The tag taxonomy is now a simple flat list.

Updated

Section 12 (Tags) — completely rewritten to reflect flat tag structure. Removed hierarchical examples and references to “tag tree” and “nesting levels”.
All examples — converted from hierarchical tags to flat tag lists (stdio-server, http-server, full-featured examples in both JSON and YAML formats).

[0.6.0] — 2026-03-20

Removed

Removed the metadata object from the root document structure. The authors, documentation, and repository fields are redundant with info.contact and info.websiteUrl, or belong in vendor extensions.
Removed the lifecycle object from the root document structure. Server lifecycle management belongs in a server manifest or registry, not in a static capability description.

Added

Root-level tags array with structured Tag Objects (name, description, tags) replacing metadata.tags. Tags support hierarchical nesting via nested tags arrays (Option C). Tag names MUST be globally unique across the entire tree.
Tag reference validation requirement — per-entity tags on tools, resources, resource templates, and prompts MUST reference tag names declared in the root tags array when present. Undeclared tag references are a validation error.

Changed

Section 12 rewritten from “Metadata” to “Tags” — defines the Tag Object, uniqueness constraints, and tag reference semantics.
Sections 9, 10, 11 — per-entity tags description updated with normative cross-reference to Section 12.3 tag declaration requirement.
Section 3 root object table — metadata and lifecycle rows removed; tags row added.
Sections renumbered — removal of lifecycle (formerly Section 12) shifts Tags to 12, Specification Extensions to 13, Serialization to 14, Conformance to 15.

[0.5.2] — 2026-03-18

Changed

Documented MCP Implementation type provenance in the Info Object — name, title, description, version, icons, and websiteUrl are now explicitly traced to the MCP Implementation type returned in the initialize response (serverInfo), with protocol version annotations:
- title — MCP BaseMetadata, since 2025-06-18
- description — MCP Implementation, since 2025-06-18
- websiteUrl — MCP Implementation, since 2025-11-25
- icons — MCP Implementation (via Icons mixin), since 2025-11-25
Updated Info Object example to include icons and websiteUrl fields
Clarified contact and license as OpenAPI-style additions not present in the MCP Implementation type

[0.5.1] — 2026-03-17

Changed

Removed _generated from the core MCP Description specification (mcpdesc: "0.5.1"), including the root object definition and current schema.
Updated Cisco extension to x-cisco-metadata v0.2.0 shape with extension-level version and nested dump payload
Removed _generated from Cisco extension examples, with provenance retained in x-cisco-metadata.dump (toolName, toolVersion, createdAt)

[0.5.0] — 2026-03-17

Changed

Renamed transport field to transports (plural) for consistency with tools, resources, prompts and OpenAPI’s servers — see DECISION-001
Added transport-scoped security — each transport MAY include its own security array that overrides the root-level default (see Section 6.4)
Root-level security is now the default; transport-level security overrides it (OpenAPI-style inheritance)

[0.4.0] — 2026-03-16

Added

MCP 2025-11-25 support: icons, websiteUrl, task capabilities, tool execution properties
Tool outputSchema with explicit $schema dialect support (MCP 2025-06-18+)
Tool execution.taskSupport property for task-augmented execution (MCP 2025-11-25+)
icons definition for server, tools, resources, resource templates, and prompts
capabilities.tasks for task-augmented request support
capabilities.completions and capabilities.logging declarations

Changed

Renamed mcpspec field to mcpdesc to clearly distinguish the description format version from the MCP protocol specification version
protocolVersion enum now includes 2025-11-25
Tool annotations now supports additionalProperties for forward compatibility

[0.3.0] — 2026-01-15

Added

title field on all MCP entities (BaseMetadata, since MCP 2025-06-18)
Tool outputSchema for structured tool output
_meta protocol-reserved metadata on tools, resources, resource templates, and prompts
tags for categorization on tools, resources, resource templates, and prompts
deprecated flag on tools, resources, resource templates, and prompts

Changed

Aligned more closely with MCP 2025-06-18 protocol structures

[0.1.0] — 2025-11-01

Added

Initial specification draft
Core document structure: mcpspec, info, transport, tools, resources, resourceTemplates, prompts
Transport definitions: streamable-http, stdio, sse
Security schemes aligned with OpenAPI 3.1
capabilities object from MCP InitializeResult
metadata for authors, documentation, repository, tags
_generated provenance tracking
Specification extension mechanism (x- prefix)
anyOf constraint requiring at least one of tools, resources, resourceTemplates, or prompts