YourAITools MCP Hub

ToolFit: Preflight a remote MCP server (MCPCheck)

check_mcp_server

Read-onlyIdempotent

Does this remote MCP server work, and is it worth connecting or paying for? Sends initialize and tools/list only (never calls a tool) and reports reachability, protocol version, sign-in method (OAuth protected-resource metadata), x402 payment terms if it asks for payment, latency, tool count and token cost, provider compatibility, poisoning patterns in tools and server instructions, issues and a grade A-F, plus a pin for later diffs. https public hosts only. Free: 10 checks/day per IP, then $0.005 via x402 or credits.

[ToolFit via YourAITools MCP Hub] Free tier: same as ToolFit's own MCP server (call without payment and without tier). Paid: check $0.005 per call, with a credits key (Authorization: Bearer yatc_...) or x402 (USDC; the hub returns the payment terms). Failed tool calls aren't charged: credits are refunded automatically and x402 payments only settle on success.

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": {
      "url": "<url>"
    },
    "name": "check_mcp_server"
  }
}

Input Schema

Name	Required	Description	Default
`url`	Yes	Public remote MCP server URL (Streamable HTTP, https), e.g. https://api.youraitools.co/mcp/hub. ToolFit only lists its tools.
`tier`	No	Paid tier: check $0.005. Omit tier (with no credits key or x402 payment) to use the free tier.

Schema Changelog

Changes observed during successful MCP inspections.

Changed1 schema field changedOct 30, 2026
- addedInput schema / properties / url / examples
```
Added value: +[
+  "https://api.youraitools.co/mcp/hub"
+]
```
AddedOct 24, 2026

TDQS

A4.6/5.0

Behavior5/5

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

Annotations already declare readOnly/idempotent/non-destructive, yet the description adds substantial value beyond them: precise protocol calls sent, the full report contents, rate limits, refund semantics on failure, and payment mechanics. This is exactly the kind of behavioral context that annotations cannot convey.

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 question and the key constraint, then the report contents. It is somewhat long due to a second paragraph of billing detail, but every sentence about charges, refunds, and free tiers earns its place for a paid tool.

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?

No output schema exists, so the description must describe return values — and it does so exhaustively (reachability, protocol version, auth method, latency, tool count, token cost, compatibility, poisoning, issues, grade, pin). An agent has everything needed to call and interpret the result.

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% and the schema documents both params, so baseline is 3. The description adds real meaning: 'https public hosts only,' 'ToolFit only lists its tools,' and the free-vs-paid tier behavior (omit tier to use free), which clarifies when a caller should set `tier`.

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 up front ('Does this remote MCP server work?') and enumerates exactly what it inspects: reachability, protocol version, sign-in method, x402 terms, latency, tool count, token cost, poisoning patterns, and an A-F grade. The read-only 'initialize and tools/list only (never calls a tool)' scope clearly separates it from siblings like audit_tools or scan_tools that might act on content.

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

Usage Guidelines4/5

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

Gives strong context: use before connecting/paying, https public hosts only, free tier 10 checks/day then paid. The 'pin for later diffs' hints at diff_tools, but it never explicitly contrasts with watch_mcp_server (continuous monitoring) or check_x402_endpoint, so the agent must infer those boundaries.

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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