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Configuration

Selectors

Selectors control which commands and flags become MCP tools. Ophis evaluates selectors in order and uses the first matching selector for each command. If no selectors match a command, the command is not exposed as a MCP tool.

Default Behavior

  • If Config.Selectors is nil/empty, all commands and flags are exposed
  • If Config.DefaultEnv is nil, no default environment variables are added to editor configs
  • If CmdSelector is nil, the selector matches all commands
  • If LocalFlagSelector or InheritedFlagSelector is nil, all flags are included

Automatic Filtering

Always filtered regardless of configuration:

  • Hidden and deprecated commands/flags
  • Non-runnable commands (no Run/RunE)
  • Built-in commands (the cobrax command, help, completion). The cobrax command name defaults to "mcp" but can be changed via Config.CommandName

DefaultEnv

Editors like Claude Desktop, VSCode, and Cursor launch MCP server subprocesses with a minimal environment. On macOS this typically means a PATH of just /usr/bin:/bin:/usr/sbin:/sbin, which cannot find executables managed by mise, asdf, homebrew, nix, or installed to non-standard paths.

DefaultEnv specifies environment variables that are automatically included when enable writes a server config for any editor. These are merged with user-provided --env values; user values take precedence on conflict.

Capture PATH

The most common use is to capture the current shell's PATH so the MCP server subprocess can find tools like helm, kubectl, docker, terraform, etc.:

config := &cobrax.Config{
    DefaultEnv: map[string]string{
        "PATH": os.Getenv("PATH"),
    },
}

Multiple Variables

config := &cobrax.Config{
    DefaultEnv: map[string]string{
        "PATH":       os.Getenv("PATH"),
        "KUBECONFIG": os.Getenv("KUBECONFIG"),
        "HOME":       os.Getenv("HOME"),
    },
}

User Override

User-provided --env values always take precedence over DefaultEnv:

# Uses DefaultEnv PATH
./my-cli mcp claude enable

# Overrides DefaultEnv PATH with user value, keeps other DefaultEnv vars
./my-cli mcp claude enable --env PATH=/custom/path

Examples

Expose Specific Commands

config := &cobrax.Config{
    Selectors: []cobrax.Selector{
        {
            CmdSelector: cobrax.AllowCmds("kubectl get", "kubectl describe"),
        },
    },
}

Exclude Sensitive Flags

config := &cobrax.Config{
    Selectors: []cobrax.Selector{
        {
            LocalFlagSelector: cobrax.ExcludeFlags("token", "password"),
            InheritedFlagSelector: cobrax.NoFlags,
        },
    },
}

Different Rules per Command Type

config := &cobrax.Config{
    Selectors: []cobrax.Selector{
        {
            // Read ops: timeout
            CmdSelector: cobrax.AllowCmdsContaining("get", "list"),
            Middleware: func(ctx context.Context, req *mcp.CallToolRequest, in cobrax.ToolInput, next func(context.Context, *mcp.CallToolRequest, cobrax.ToolInput) (*mcp.CallToolResult, cobrax.ToolOutput, error)) (*mcp.CallToolResult, cobrax.ToolOutput, error) {
                ctx, cancel := context.WithTimeout(ctx, time.Minute)
                defer cancel()
                return next(ctx, req, in)
            },
        },
        {
            // Write ops: restrict flags
            CmdSelector: cobrax.AllowCmdsContaining("delete", "apply"),
            LocalFlagSelector: cobrax.ExcludeFlags("force", "all"),
        },
    },
}

Selector Functions

Commands

  • AllowCmds(cmds ...string) - Exact matches
  • ExcludeCmds(cmds ...string) - Exact exclusions
  • AllowCmdsContaining(substrings ...string) - Contains any
  • ExcludeCmdsContaining(substrings ...string) - Excludes all

Flags

  • AllowFlags(names ...string) - Include only these
  • ExcludeFlags(names ...string) - Exclude these
  • NoFlags - Exclude all

Custom Selector Functions

config := &cobrax.Config{
    Selectors: []cobrax.Selector{
        {
            CmdSelector: func(cmd *cobra.Command) bool {
                // Only expose commands that have been annotated as "mcp"
                return cmd.Annotations["mcp"] == "true"
            },

            LocalFlagSelector: func(flag *pflag.Flag) bool {
                return flag.Annotations["mcp"] == "true"
            },

            InheritedFlagSelector: func(flag *pflag.Flag) bool {
                return flag.Annotations["mcp"] == "true"
            },
        },
    },
}

Middleware

Wrap execution with custom logic:

Middleware: func(ctx context.Context, req *mcp.CallToolRequest, in cobrax.ToolInput, next func(context.Context, *mcp.CallToolRequest, cobrax.ToolInput) (*mcp.CallToolResult, cobrax.ToolOutput, error)) (*mcp.CallToolResult, cobrax.ToolOutput, error) {
    // Pre-execution: Add timeout
    ctx, cancel := context.WithTimeout(ctx, 30*time.Second)
    defer cancel()

    // Pre-execution: Validate input
    if len(in.Args) > 10 {
        in.Args = in.Args[:10]
    }

    // Execute the command
    res, out, err := next(ctx, req, in)

    // Post-execution: Filter output
    if strings.Contains(out.StdOut, "SECRET") {
        out.StdOut = "[REDACTED]"
    }

    return res, out, err
}

Tool Annotations

Set MCP tool annotations on Cobra commands using cmd.Annotations. These hints help AI clients make informed decisions about tool invocation.

Available Annotation Keys

Key Type Description
cobrax.AnnotationTitle ("title") string Human-readable title for the tool
cobrax.AnnotationReadOnly ("readOnlyHint") bool Tool does not modify its environment
cobrax.AnnotationDestructive ("destructiveHint") bool Tool may perform destructive updates
cobrax.AnnotationIdempotent ("idempotentHint") bool Repeated calls have no additional effect
cobrax.AnnotationOpenWorld ("openWorldHint") bool Tool may interact with external entities

Boolean values are parsed with strconv.ParseBool ("true", "1", "t", "false", "0", "f", etc.). Invalid values are skipped with a warning.

Example

listCmd := &cobra.Command{
    Use:   "list",
    Short: "List all resources",
    Annotations: map[string]string{
        cobrax.AnnotationTitle:    "List Resources",
        cobrax.AnnotationReadOnly: "true",
    },
}

deleteCmd := &cobra.Command{
    Use:   "delete [id]",
    Short: "Delete a resource",
    Annotations: map[string]string{
        cobrax.AnnotationTitle:       "Delete Resource",
        cobrax.AnnotationDestructive: "true",
        cobrax.AnnotationIdempotent:  "true",
        cobrax.AnnotationOpenWorld:   "false",
    },
}

Logging

config := &cobrax.Config{
    SloggerOptions: &slog.HandlerOptions{
        Level: slog.LevelDebug,
    },
}

Or via CLI:

./my-cli mcp vscode enable --log-level debug