# AB-021: MCP Tool Calls | AgentBadge

> Your MCP server responds when agents try to call a tool.

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 [Machine-Readable](https://agentbadge.xyz/rules#machine_readable)
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 AB-021

 📞

AB-021

# MCP Tool Calls

 [🤖 Machine-Readable](https://agentbadge.xyz/rules#machine_readable)

 Pillar: Discovery

 Moderate effort

 Severity: high

 Est. cost: $10-50

 Gap: documentation

 Fix: deterministic

## What it means

Your MCP server responds when agents try to call a tool.

## Why it matters

Listing tools isn't enough — agents need to actually call them. If calls fail, your MCP server is useless.

## Evidence expected

This rule is verified by:

 http

 Source: Website content

 ✗

### What's wrong

MCP server lists tools but doesn't respond when agents try to use them.

 ✓

### What's right

MCP server processes tool calls and returns results.

## Check this rule on your site

Enter your URL to check just this one rule (AB-001).

 Check rule

## Related rules in Machine-Readable

 [💲
 Machine-Readable Pricing](https://agentbadge.xyz/rules/AB-010)
 [⏱️
 Rate Limits Declared](https://agentbadge.xyz/rules/AB-011)
 [⚠️
 Structured Error Responses](https://agentbadge.xyz/rules/AB-012)
 [🛠️
 MCP Tools List](https://agentbadge.xyz/rules/AB-020)
 [📡
 MCP Streaming Support](https://agentbadge.xyz/rules/AB-022)

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## Machine-Readable

 This rule is also available as JSON:
 [/rules/AB-021.json](https://agentbadge.xyz/rules/AB-021.json)

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