spring-projects/spring-ai · error · IllegalArgumentException

Either prompt or uri must be provided!

Error message

Either prompt or uri must be provided!

What it means

AbstractMcpCompleteMethodCallback's constructor requires that a completion callback provide exactly one completion target: either a prompt name or a resource URI. When both are absent (null or empty), it throws this IllegalArgumentException at registration time because the callback would have nothing to complete against.

Source

Thrown at mcp/mcp-annotations/src/main/java/org/springframework/ai/mcp/annotation/method/complete/AbstractMcpCompleteMethodCallback.java:87

	/**
	 * Constructor for AbstractMcpCompleteMethodCallback.
	 * @param method The method to create a callback for
	 * @param bean The bean instance that contains the method
	 * @param prompt The prompt reference
	 * @param uri The URI reference
	 * @param uriTemplateManagerFactory The URI template manager factory
	 */
	protected AbstractMcpCompleteMethodCallback(Method method, Object bean, String prompt, String uri,
			McpUriTemplateManagerFactory uriTemplateManagerFactory) {

		Assert.notNull(method, "Method can't be null!");
		Assert.notNull(bean, "Bean can't be null!");
		Assert.notNull(uriTemplateManagerFactory, "URI template manager factory can't be null!");

		// Either prompt or uri must be provided, but not both
		if ((prompt == null || prompt.isEmpty()) && (uri == null || uri.isEmpty())) {
			throw new IllegalArgumentException("Either prompt or uri must be provided!");
		}
		if ((prompt != null && !prompt.isEmpty()) && (uri != null && !uri.isEmpty())) {
			throw new IllegalArgumentException("Only one of prompt or uri can be provided!");
		}

		this.method = method;
		this.bean = bean;
		this.prompt = prompt;
		this.uri = uri;

		// Create the CompleteReference based on prompt or uri
		if (prompt != null && !prompt.isEmpty()) {
			this.completeReference = McpSchema.PromptReference.builder(prompt).build();
		}
		else {
			this.completeReference = new McpSchema.ResourceReference(uri);
		}

View on GitHub (pinned to 98a7beda4f)

Solutions

1. Set the prompt attribute if the completion is for a prompt: e.g. prompt = "myPrompt".
2. Set the uri attribute instead if the completion is for a resource template: e.g. uri = "file:///documents/{path}".
3. Ensure exactly one of the two is populated (see error 84 for the both-set case).

Example fix

// before
new AbstractMcpCompleteMethodCallback(method, bean, null, null, factory); // throws
// after
new AbstractMcpCompleteMethodCallback(method, bean, "myPrompt", null, factory);

boolean hasPrompt = prompt != null && !prompt.isEmpty();
boolean hasUri = uri != null && !uri.isEmpty();
if (!hasPrompt && !hasUri) throw new IllegalStateException("set either prompt or uri for @McpComplete");

try {
    registry.registerCompleteCallback(method, bean, prompt, uri);
} catch (IllegalArgumentException e) {
    LOG.error("completion registration failed: {}", e.getMessage());
}

When it happens

Trigger: Registering an @McpComplete-annotated completion method without setting either the prompt attribute or the uri attribute (both null/empty) in the specification or annotation.

Common situations: Forgetting the prompt attribute when moving from resource completion to prompt completion; copying a builder call and deleting both attributes; annotation processor not picking up default attribute values.

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

• Method must return either CompleteResult, CompleteCompletion
• Method must have exactly 1 parameter (List<McpSchema.Resourc
• Method must have void or Mono<Void> return type:
• Method must have void return type: " + method.getName() + "
• clients must not be empty

AI-assisted analysis of spring-projects/spring-ai@98a7beda4f (2026-09-11). Data as JSON: /api/errors/bfef19ad6d9ad37b. Report an issue: GitHub.