# MCP Server Tester — Validate Your MCP Server Before You Ship

> Free browser-based MCP server tester. Validate tool schemas, exercise `tools/call` with real arguments, watch raw JSON-RPC frames, and catch protocol bugs before you publish.

**Source:** https://mcpplaygroundonline.com/mcp-server-tester

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## Who this is for

MCP server *developers* — people who are writing a server and need to know it is correct before it reaches a client. If you want to drive someone else's server with an AI agent instead, use [Agent Studio](https://mcpplaygroundonline.com/mcp-agent-studio).

## What it checks

- **Connection and handshake** — does `initialize` succeed, and what capabilities does the server negotiate?
- **Discovery** — `tools/list`, `prompts/list`, `resources/list`, including pagination.
- **Tool schemas** — are the declared input schemas well-formed and complete enough for a model to construct arguments from?
- **Execution** — call any tool with arguments you supply and inspect the full result.
- **Raw protocol** — every JSON-RPC frame, in both directions, as it goes over the wire. This is usually where the real bug is.

## Why raw frames matter

Most MCP bugs are not logic bugs, they are protocol bugs: a malformed `content` array, a missing `isError`, a tool result that is technically valid JSON-RPC but unusable by a model. A client that hides the frames hides the bug. This tester shows them.

## Typical workflow

1. Paste your server URL (http or SSE transport).
2. Confirm the handshake and check the negotiated capabilities.
3. Walk the tool list and read each schema as a model would see it.
4. Call the tools that matter with realistic arguments.
5. When it passes here, run [evals](https://mcpplaygroundonline.com/mcp-evals) to confirm an agent can actually use it, and the [security scanner](https://mcpplaygroundonline.com/mcp-security-scanner) before you expose it publicly.

## Related

- [MCP Inspector Online](https://mcpplaygroundonline.com/mcp-inspector-online) — same connection, framed as the browser equivalent of `npx @modelcontextprotocol/inspector`.
- [MCP Test Client](https://mcpplaygroundonline.com/mcp-test-client) — the inverse: validate a *client* against hosted mock servers.
- [Mock MCP Servers](https://mcpplaygroundonline.com/mock-mcp-servers) — known-good and known-bad endpoints to test your tooling against.

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_Canonical page: https://mcpplaygroundonline.com/mcp-server-tester_

_MCP Playground (mcpplaygroundonline.com) is a free, browser-based toolkit for the Model Context Protocol: test any remote MCP server, run evals that prove an AI agent can use its tools, build reusable agents across 60+ models, and audit servers for security issues. No install, no local Node, free to start._