siyuan-note/siyuan · error

second argument must be a config object

Error message

second argument must be a config object

What it means

The second argument to registerCapability() was not usable as a config object (it was a non-object value such as a string, number, boolean, or null). The runtime calls ToObject on argument 1 and rejects the call when it is not a usable object, because all capability metadata (description, schemas) is read from it.

Solutions

1. Pass a plain object literal as the second argument: { description, inputSchema, ... }
2. Parse JSON strings into objects before passing (JSON.parse)
3. Check that the config variable is defined and typeof === "object"

Example fix

// before
plugin.registerCapability("search", JSON.stringify(config), handler);
// after
plugin.registerCapability("search", config, handler);

if (config === null || typeof config !== "object" || Array.isArray(config)) { throw new TypeError("config must be a plain object"); }

const isConfigObject = (v) => v != null && typeof v === "object" && !Array.isArray(v);

try { plugin.registerCapability(name, config, handler); } catch (e) { if (String(e).includes("second argument must be a config object")) { throw new TypeError("Pass a plain object as the 2nd argument, not " + typeof config); } throw e; }

When it happens

Trigger: registerCapability(name, "description string", handler); registerCapability(name, null, handler); or passing the handler as the second argument with only two arguments total.

Common situations: Passing a JSON string instead of a parsed object; argument order mistakes when the handler is placed second; a config variable that failed to load and is null/undefined.

Understand the failure class

Background: "Must be a positive integer", "Invalid value", "Unsupported": the invalid-argument-value error family, when a library rejects the value you pass — this error's family across 35 libraries.

Related errors

• first argument must be a tool name string
• third argument must be a handler function
• capability name must not be empty
• config.description is required and must be a string
• config.description must not be empty

AI-assisted analysis of siyuan-note/siyuan@9f775e8a12 (2026-09-19). Data as JSON: /api/errors/ee1f5ef2b575cd2a. Report an issue: GitHub.

Appendix: source

Thrown at kernel/plugin/api_agent.go:125

						}
						if outputSchemaValue := configObj.Get("outputSchema"); isJsValueNotNull(outputSchemaValue) {
							if outputSchema, err = jsCapabilitySchemaToGoSchema(rt, outputSchemaValue); err != nil {
								return
							}
						}
						if effectsValue := configObj.Get("effects"); isJsValueNotNull(effectsValue) {
							if effects, err = jsCapabilityEffectsToGoEffects(rt, effectsValue); err != nil {
								return
							}
						}
						if actionEffectsValue := configObj.Get("actionEffects"); isJsValueNotNull(actionEffectsValue) {
							if actionEffects, err = jsCapabilityActionEffectsToGoEffects(rt, actionEffectsValue); err != nil {
								return
							}
						}
					}
				} else {
					err = fmt.Errorf("second argument must be a config object")
					return
				}
				if fn, ok := goja.AssertFunction(call.Argument(2)); ok {
					handler = fn
				} else {
					err = fmt.Errorf("third argument must be a handler function")
					return
				}
				return
			}
		}()

		runErr := p.worker.Run(func(rt *goja.Runtime) (result any, err error) {
			if argErr != nil {
				err = argErr
				return
			}

View on GitHub (pinned to 9f775e8a12)