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Testing MCP Agents¶

How to test MCP Mesh agents using meshctl and curl

Note: This page shows Python examples. See meshctl man testing --typescript for TypeScript or meshctl man testing --java for Java/Spring Boot examples.

Quick Way: meshctl call¶

meshctl call hello_mesh_simple                    # Call tool by name (recommended)
meshctl call add '{"a": 1, "b": 2}'               # With arguments
meshctl list --tools                              # List all available tools

See meshctl man cli for more CLI commands.

Protocol Details: curl¶

MCP agents expose a JSON-RPC 2.0 API over HTTP with Server-Sent Events (SSE) responses. This section shows the correct curl syntax - useful for understanding the underlying protocol.

Key Points¶

Endpoint: Always POST to /mcp (not REST-style paths like /tools/list)
Method: Always POST
Headers: Must include both Content-Type AND Accept headers
Body: JSON-RPC 2.0 format with jsonrpc, id, method, params
Response: Server-Sent Events format, requires parsing

List Available Tools¶

curl -s -X POST http://localhost:PORT/mcp \
  -H "Content-Type: application/json" \
  -H "Accept: application/json, text/event-stream" \
  -d '{
    "jsonrpc": "2.0",
    "id": 1,
    "method": "tools/list",
    "params": {}
  }'

Call a Tool (No Arguments)¶

curl -s -X POST http://localhost:PORT/mcp \
  -H "Content-Type: application/json" \
  -H "Accept: application/json, text/event-stream" \
  -d '{
    "jsonrpc": "2.0",
    "id": 1,
    "method": "tools/call",
    "params": {
      "name": "get_current_time",
      "arguments": {}
    }
  }'

Call a Tool (With Arguments)¶

curl -s -X POST http://localhost:PORT/mcp \
  -H "Content-Type: application/json" \
  -H "Accept: application/json, text/event-stream" \
  -d '{
    "jsonrpc": "2.0",
    "id": 1,
    "method": "tools/call",
    "params": {
      "name": "generate_report",
      "arguments": {"title": "Test Report", "format": "markdown"}
    }
  }'

Available MCP Methods¶

Method	Description
`tools/list`	List all available tools
`tools/call`	Invoke a tool with arguments
`prompts/list`	List available prompts
`resources/list`	List available resources
`resources/read`	Read a resource

Response Format¶

MCP responses use Server-Sent Events (SSE) format:

data: {"jsonrpc":"2.0","id":1,"result":{"tools":[...]}}

To parse the response, you can pipe through:

| grep "^data:" | sed 's/^data: //' | jq .

Common Errors¶

Missing Accept Header¶

Error: Response not in expected format
Fix: Add -H "Accept: application/json, text/event-stream"

Wrong Endpoint¶

Error: 404 Not Found
Fix: Use /mcp endpoint, not /tools/list or similar

Invalid JSON-RPC Format¶

Error: Invalid request
Fix: Ensure body has jsonrpc, id, method, and params fields

Testing in Docker Compose¶

Calls route through the registry proxy by default:

meshctl call greet
meshctl call add '{"a": 1, "b": 2}'

# Bypass proxy (requires mapped ports)
meshctl call greet --use-proxy=false --agent-url http://localhost:9001

Testing in Kubernetes¶

For Kubernetes with ingress configured, use ingress mode:

# With DNS configured for the ingress domain
meshctl call greet --ingress-domain mcp-mesh.local

# Without DNS (direct IP or port-forwarded)
meshctl call greet --ingress-domain mcp-mesh.local --ingress-url http://localhost:9080

Testing with meshctl¶

# Find agent ports
meshctl list

# Check agent status
meshctl status --verbose