Fixter

Detect MCP Protocol

detect_mcp_protocol

Read-onlyIdempotent

Probe a remote MCP server once over every protocol revision (2026-07-28 stateless, 2025-11-25 / 2025-06-18 / 2025-03-26 with sessions, 2024-11-05 HTTP+SSE) and report which it accepts, with the HTTP status, content type and first bytes for each it does not. Outcomes: DETECTED, AUTH_REQUIRED (the server refused the probe with HTTP 401, 402 or 403 on at least one revision and accepted none; pass a credential to see which revisions it speaks, or create the test with mcpTier UPTIME to check only that it is up), RATE_LIMITED, NONE. Use this before create_api_test to choose mcpProtocolRevision: ANY (the default) checks that the endpoint answers as an MCP server without asserting a revision; NEWEST_SUPPORTED follows the newest revision the server speaks; a dated revision pins the test to it. Makes up to seven requests to the server on the customer's behalf.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "mcpUrl": "<mcpUrl>"
    },
    "name": "detect_mcp_protocol"
  }
}

Input Schema

Name	Required	Description	Default
`mcpUrl`	Yes	The http(s) URL of the MCP server to probe
`mcpCredentialId`	No	Id of a stored credential from list_api_test_credentials, for a server that needs authentication

Schema Changelog

Changes observed during successful MCP inspections.

AddedOct 22, 2026

TDQS

A4.8/5.0

Behavior5/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already cover safety (readOnly, idempotent, non-destructive), and the description adds genuinely new context: it discloses that up to seven requests are made to the customer's server, enumerates the four terminal outcomes, and explains what is returned on failure. The AUTH_REQUIRED branch even explains the triggering HTTP codes (401/402/403).

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Front-loaded with the core action and outcome list, and each subsequent clause carries real information (outcome semantics, revision mapping, request count). It is dense and long-sentenced, but very little of it is filler.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

There is no output schema, so the description carries the return-value burden — and it does, naming all four outcomes and the per-revision failure payload. Combined with the request-count disclosure and the downstream revision mapping, an agent has everything needed to call and interpret it.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters4/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100%, so both parameters are already documented. The description still adds meaning beyond the schema by explaining what mcpCredentialId unlocks behaviorally — that supplying a credential reveals which revisions the server actually speaks rather than returning AUTH_REQUIRED.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb and resource (probe a remote MCP server across every protocol revision) and names the exact output: which revisions are accepted plus status/content-type/first-bytes for those rejected. It is clearly distinct from sibling tools like create_api_test, which it explicitly positions itself ahead of.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines5/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Gives explicit sequencing guidance ('Use this before create_api_test to choose mcpProtocolRevision') and explains how each resulting value maps to a choice (ANY vs NEWEST_SUPPORTED vs dated revision). It also names alternatives for the auth-blocked case: pass a credential, or create the test with mcpTier UPTIME.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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