micro/go-micro · error

key is required

Error message

key is required

What it means

The built-in store "read" MCP tool requires the "key" input parameter identifying the store record to fetch. An empty or missing key fails the guard before store.Read is called.

Solutions

1. Pass a non-empty "key" string in the tool input: {"key": "user:123"}.
2. If you need a listing, check whether the store implementation offers a list capability instead of calling read with an empty key.
3. Validate that the key value is non-empty in the client before invoking the tool.

Example fix

// before
input := map[string]interface{}{} // no key
// after
input := map[string]interface{}{"key": "user:123"}

key, _ := input["key"].(string)
if key == "" {
    return errors.New("store read requires a non-empty 'key' argument")
}

func validKey(input map[string]interface{}) (string, bool) {
    k, ok := input["key"].(string)
    return k, ok && k != ""
}

records, err := callTool("store_read", map[string]interface{}{"key": key})
if err != nil {
    if strings.Contains(err.Error(), "key is required") {
        // supply the key and retry
    }
}

When it happens

Trigger: An MCP client calls the store read tool with input {} or {"key": ""}; the handler short-circuits with "key is required" instead of reading from the store.

Common situations: LLM omits the key argument; caller assumed the tool would list all records instead of reading by key; key variable was empty because upstream data was missing.

Understand the failure class

Background: "missing required argument" and "the following required arguments were not provided": what required-argument errors mean and how to fix them — this error's family across 20 libraries.

Related errors

• name is required
• topic is required
• addr (nats subject) must not be empty
• addr (nats subject) must not contain space characters
• ai model is nil

AI-assisted analysis of micro/go-micro@24529f1404 (2026-09-01). Data as JSON: /api/errors/7edabca405cca774. Report an issue: GitHub.

Appendix: source

Thrown at gateway/mcp/mcp.go:495

				return nil, err
			}
			return map[string]interface{}{"keys": keys}, nil
		},
	})

	addFramework(&Tool{
		Name:        "micro_store_read",
		Description: "Read a record from the data store by key",
		InputSchema: map[string]interface{}{
			"type": "object",
			"properties": map[string]interface{}{
				"key": map[string]interface{}{"type": "string", "description": "Record key"},
			},
		},
		Handler: func(input map[string]interface{}) (interface{}, error) {
			key, _ := input["key"].(string)
			if key == "" {
				return nil, fmt.Errorf("key is required")
			}
			records, err := store.Read(key)
			if err != nil {
				return nil, err
			}
			if len(records) == 0 {
				return map[string]interface{}{"error": "not found"}, nil
			}
			return map[string]interface{}{"key": key, "value": string(records[0].Value)}, nil
		},
	})

	addFramework(&Tool{
		Name:        "micro_store_write",
		Description: "Write a record to the data store",
		InputSchema: map[string]interface{}{
			"type": "object",
			"properties": map[string]interface{}{

View on GitHub (pinned to 24529f1404)