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retoor 251c3dc2ba research: mcp-client-support subject (106 sources, 3 conclusions)

- wire spec: lifecycle, stdio + Streamable HTTP transports, tools,
  utilities, legacy SSE, versioning, changelog (14 Tier 1)
- client ecosystem: Claude Code/VS Code/Cursor/Codex configs,
  mcp-remote, Smithery, registries, Glama (12 Tier 1)
- security/ops: authorization draft, trust model, poisoning,
  rug pulls, production hardening (12 Tier 1) + 68 Tier 2 cards
- conclusions: minimal stdlib client on 2025-11-25, normalizer +
  resolver agent for pasted configs/GitHub URLs, untrusted-until-
  consent trust model; nothing built yet
- audit PASS (14 subjects, 797 sources, 32 conclusions)

2026-10-18 19:23:02 +02:00

3.8 KiB

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Tools: tools/list + tools/call + error split (2025-11-25)

Metadata

Field	Value
Institute	Molodetz Institute - Research & Retrieval Division
Subject	mcp-client-support
Document type	Source Dossier
Tier	1
Source title	Tools (MCP Specification v2025-11-25)
Source URL	https://modelcontextprotocol.io/specification/2025-11-25/server/tools
Source publisher / author	Model Context Protocol authors (Anthropic-donated open project; site docs)
Source type	standard
Source date (published)	2025-11-25 (version stamp; no other publish date stated)
Date researched	2026-10-18
Researched by	tai (agent), model: Claude Sonnet 5, on behalf of retoor
Research method	gather-subagent direct page fetch, parent synthesis from evidence pack
Confidence	High
Status	Active

Summary

This page defines the server tools feature: capability declaration with optional listChanged, paginated tools/list, and tools/call with name/arguments params returning content plus isError. Its central point for clients is the two-track error model: protocol errors are standard JSON-RPC errors (for example unknown tools), while tool execution failures arrive as successful results with isError: true. It also lists content types (text, image, audio, resource_link, embedded resource, optional structuredContent) and client security guidance.

Key findings

"Servers that support tools MUST declare the tools capability", with optional listChanged.
tools/list "supports pagination" (cursor param, nextCursor in result).
tools/call params: {"name": …, "arguments": {…}}; result: {"content": […], "isError": false}.
"Tools use two error reporting mechanisms: 1. Protocol Errors: Standard JSON-RPC errors… Unknown tools… 2. Tool Execution Errors: Reported in tool results with isError: true"; "Clients SHOULD provide tool execution errors to language models."
Protocol-error example: {"code": -32602, "message": "Unknown tool: invalid_tool_name"}.
Unstructured content types: text, image (base64 plus mimeType), audio, resource_link, embedded resource; plus optional structuredContent object validated against outputSchema when present.
Client security guidance: "Implement timeouts for tool calls", "Validate tool results before passing to LLM", "treat tool annotations as untrusted."

Pros / strengths

The JSON-RPC-error vs isError: true split is stated normatively with examples, which is exactly the distinction a client must get right to avoid misrouting tool failures as transport faults.
Request and result shapes are given literally (name/arguments, content/isError, cursor/nextCursor), so the data plane is implementable without inference.
Security guidance is client-actionable (timeouts, result validation, untrusted annotations) rather than vague.

Cons / limitations / caveats

No explicit author names or publish dates appear on the page; the date above is the version stamp in the URL, per the pack's Uncertainty notes.
Content-type breadth (image, audio, resource_link, embedded resource, structuredContent with outputSchema validation) means a minimal client must decide up front how much result rendering to support versus passing through.
listChanged notification handling and outputSchema validation are extra client work beyond the two-method core, not covered in depth here.

Relevance to tai

This is the entire tools data plane for a minimal client: two methods, a pagination loop, and the critical JSON-RPC-error vs isError: true distinction. Combined with the lifecycle handshake, this page plus transports is nearly the whole minimal-client spec.

Changelog

Date	Change
2026-10-18	Initial dossier created.

3.8 KiB Raw Blame History