_meta Property on CallToolResult Use is Unclear · Issue #264 · modelcontextprotocol/modelcontextprotocol · GitHub Skip to content Navigation Menu Sign in Appearance settings * Platform * AI CODE CREATION * GitHub Copilot Write better code with AI * GitHub Copilot app Direct agents from issue to merge * MCP Registry Integrate external tools * DEVELOPER WORKFLOWS * Actions Automate any workflow * Codespaces Instant dev environments * Issues Plan and track work * Code Review Manage code changes * Code Quality Enforce quality at merge * APPLICATION SECURITY * GitHub Advanced Security Find and fix vulnerabilities * Code security Secure your code as you build * Secret protection Stop leaks before they start * EXPLORE * Why GitHub * Documentation * Blog * Changelog * Marketplace View all features * Solutions * BY COMPANY SIZE * Enterprises * Small and medium teams * Startups * Nonprofits * BY USE CASE * App Modernization * DevSecOps * DevOps * CI/CD * View all use cases * BY INDUSTRY * Healthcare * Financial services * Manufacturing * Government * View all industries View all solutions * Resources * EXPLORE BY TOPIC * AI * Software Development * DevOps * Security * View all topics * EXPLORE BY TYPE * Customer stories * Events & webinars * Ebooks & reports * Business insights * GitHub Skills * SUPPORT & SERVICES * Documentation * Customer support * Community forum * Trust center * Partners View all resources * Open Source * COMMUNITY * GitHub Sponsors Fund open source developers * PROGRAMS * Security Lab * Maintainer Community * GitHub Stars * Archive Program * REPOSITORIES * Topics * Trending * Collections * Enterprise * ENTERPRISE SOLUTIONS * Enterprise platform AI-powered developer platform * AVAILABLE ADD-ONS * GitHub Advanced Security Enterprise-grade security features * Copilot for Business Enterprise-grade AI features * Premium Support Enterprise-grade 24/7 support * Pricing Search / Sign in Sign up Appearance settings You signed in with another tab or window. Reload to refresh your session. You signed out in another tab or window. Reload to refresh your session. You switched accounts on another tab or window. Reload to refresh your session. Dismiss alert Uh oh! There was an error while loading. Please reload this page . modelcontextprotocol / modelcontextprotocol Public * Notifications You must be signed in to change notification settings * Fork 1.8k * Star 9.2k * Code * Issues 69 * Pull requests 78 * Discussions * Actions * Projects * Security and quality 1 * Insights Additional navigation options * Code * Issues * Pull requests * Discussions * Actions * Projects * Security and quality * Insights _meta Property on CallToolResult Use is Unclear   #264 New issue Copy link New issue Copy link Closed Closed _meta Property on CallToolResult Use is Unclear #264 Copy link Labels bug Something isn't working Something isn't working Description patwhite opened on Apr 1, 2025 Issue body actions Describe the bug The _meta property on CallToolResult has the description "This result property is reserved by the protocol to allow clients and servers to attach additional metadata to their responses." - "reserved" is generally used in specs to imply that the spec is reserving this for future definition, but I don't think that's actually correct here, I think this is meant as a free form field. The question would be - is that "reserved" in the traditional sense or is it fine to start using this today? To Reproduce N/A Expected behavior I would clarify the description to say "The result property is available for server to client communication of arbitrary data which falls outside the scope of this specification" Logs N/A Additional context N/A Reactions are currently unavailable Activity Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment Metadata Metadata Assignees No one assigned Labels bug Something isn't working Something isn't working Type No type Projects No projects Milestone No milestone Relationships None yet Development No branches or pull requests Issue actions * Open in GitHub Copilot app Footer (c) 2026 GitHub, Inc. Footer navigation * Terms * Privacy * Security * Status * Community * Docs * Contact * Manage cookies * Do not share my personal information You can’t perform that action at this time.