tool-arg-defaults

Apply per-tool default kwargs to LLM-generated tool calls. Caller-supplied values always win. null is a real value, not "use the default".

Usage

use serde_json::json;
use tool_arg_defaults::ToolDefaults;

let mut defaults = ToolDefaults::new();
defaults.register("search_web", json!({"timeout": 30, "max_results": 10}));
defaults.register("fetch", json!({"timeout": 60, "follow_redirects": true}));

// LLM only passed "q"
let merged = defaults.apply("search_web", &json!({"q": "anthropic"}), false).unwrap();
// merged == {"q": "anthropic", "timeout": 30, "max_results": 10}

// Caller-supplied timeout wins
let merged = defaults.apply("search_web", &json!({"q": "x", "timeout": 5}), false).unwrap();
// merged == {"q": "x", "timeout": 5, "max_results": 10}

Features

• register(name, json_object) sets defaults for a tool
• apply(name, args, strict) merges defaults into caller-supplied args
• Caller keys always win (including explicit null)
• strict=true raises ToolNotRegisteredError for unknown tools
• update / unregister for dynamic reconfiguration
• Zero dependencies beyond serde_json

License

MIT OR Apache-2.0