RFC: Compact User-to-Model Tool Trigger Syntax ||MCP@...||

[vital789]

Pre-submission Checklist

• I have verified this would not be more appropriate as a feature request in a specific repository
• I have searched existing discussions to avoid duplicates

Your Idea

Problem

Current MCP ecosystem lacks a standardized, token-efficient syntax for users
to explicitly request tool execution within prompts. Developers rely on
natural language ("please search for...") or framework-specific conventions,
leading to:

• Inconsistent behavior across models (Claude, GPT, Llama interpret hints differently)
• Higher token costs for explicit tool requests
• No deterministic way to force execution vs. let model decide

Proposal

Compact inline trigger syntax for user-to-model tool hints:

Auto-detect (model decides necessity):
||MCP@service:{json}||

Mandatory force call:
EXEC:||MCP@service:{json}||

Examples

||MCP@search:{"q":"weather in Tokyo"}||
||MCP@compute:{"a":157,"b":189}||
||MCP@sum:[1,2,3,4,5]||
EXEC:||MCP@log:{"event":"user_login","ts":1704067200}||

System Prompt Example

MCP-Services Tool Trigger:
If prompt has: ||MCP@service:{json}|| - call if necessary;
OR: EXEC:||MCP@service:{json}|| - force call;
call specified service by std API tool call with json params.

Syntax Specification

• Delimiter: || (double pipe, rare in natural text (single token))
• Namespace: MCP@ (prevents collision with wiki-links [[...]])
• Service slot: service (maps to MCP tool name)
• Payload: valid JSON (object or array)

Benefits

• Token efficiency: ~5 tokens vs 15-30 for natural language equivalent
• Unambiguous: || not used in Markdown/HTML/LaTeX; MCP@ namespace isolates from wiki syntax
• Deterministic: explicit EXEC: prefix removes model's discretion
• Framework-agnostic: converts to standard MCP/Function Call/OpenAI tools on backend
• Human-readable: compact yet parseable by both humans and regex

Reference Validation

Tested with: Kimi (Moonshot), GPT-4, Claude 3.5 Sonnet, Llama 3.1
Success rate: >95% for trigger recognition when specified in system prompt.

Scope

• Protocol Specification
• SDK Features
• Documentation
• Developer Experience
• Other