Lesson 5 · 20 min
Book, pay, delete: an action with consequences needs a yes from a person. In the 2026-07-28 revision, the server no longer opens its own request to ask. It returns input_required, the client asks the user, and repeats the call with the answer. In this lesson you see both rounds and the path of the no.
Start the lesson
Goal: make the tool with consequences ask for confirmation mid-call with input_required and act only after the yes.
Click each step. Your handler runs in both rounds.
Before (2025): the server started elicitation/create, sampling and roots on its own. In 2026-07-28 this became MRTR, and Sampling and Roots are deprecated.
Excerpt from kit/servidor.mjs. It is written to run on both rounds: it reads what has already arrived and asks only for what is missing.
async ({ turma_id, email }, ctx) => {
const turma = TURMAS.find(x => x.id === turma_id);
if (!turma) return { content: [{ type: 'text', text: `turma ${turma_id} não existe` }], isError: true };
if (turma.vagas < 1) return { content: [{ type: 'text', text: `turma ${turma_id} sem vagas` }], isError: true };
const resposta = inputResponse(ctx.mcpReq.inputResponses, 'confirmar');
if (resposta.kind === 'elicit' && resposta.action !== 'accept') {
return { content: [{ type: 'text', text: 'reserva cancelada pelo usuário' }], isError: true };
}
const ok = acceptedContent(ctx.mcpReq.inputResponses, 'confirmar', Confirma);
if (ok?.confirmar !== true) {
return inputRequired({
inputRequests: {
confirmar: inputRequired.elicit({ message: `Reservar 1 vaga em "${turma.titulo}" para ${email}?`, requestedSchema: Confirma })
}
});
}
turma.vagas -= 1;
return { content: [{ type: 'text', text: `reservado: ${turma_id} para ${email} (restam ${turma.vagas})` }] };
}The script shows the raw 1st round (without the client completing it on its own) and then the normal flow.
cd ~/projetos/formacao-webmcp-mcp-v72/kit node teste-confirmacao.mjs sim; echo "saída: $?"
cd ~/projetos/formacao-webmcp-mcp-v72/kit node teste-confirmacao.mjs nao; echo "saída: $?"
// teste-confirmacao.mjs — shows the MRTR (revision 2026-07-28): the reservar_vaga tool
// returns resultType "input_required"; the client asks the user and repeats the call.
// Usage: node teste-confirmacao.mjs sim (the "user" accepts)
// node teste-confirmacao.mjs nao (the "user" declines)
import { Client, StreamableHTTPClientTransport } from '@modelcontextprotocol/client';
import { createMcpHandler } from '@modelcontextprotocol/server';
import { createServer } from './servidor.mjs';
const resposta = process.argv[2] === 'nao' ? 'nao' : 'sim';
const handler = createMcpHandler(createServer);
const ligar = async extra => {
const c = new Client({ name: 'teste-confirmacao', version: '1.0.0' },
{ versionNegotiation: { mode: 'auto' }, capabilities: { elicitation: { form: {} } }, ...extra });
await c.connect(new StreamableHTTPClientTransport(new URL('http://teste.local/mcp'),
{ fetch: (url, init) => handler.fetch(new Request(url, init)) }));
return c;
};
const args = { turma_id: 'html-01', email: 'aluno@exemplo.com' };
// 1st round "by hand": what arrives from the server before the user answers.
const cru = await ligar({ inputRequired: { autoFulfill: false } });
const volta1 = await cru.request({ method: 'tools/call', params: { name: 'reservar_vaga', arguments: args } }, { allowInputRequired: true });
console.log(`1ª volta: resultType=${volta1.resultType} · pede: ${Object.keys(volta1.inputRequests ?? {}).join(', ')}`);
await cru.close();
// Normal flow: the client SDK calls your elicitation handler and repeats the call on its own.
const cliente = await ligar({});
cliente.setRequestHandler('elicitation/create', async req => {
console.log(`[cliente] pergunta ao usuário: ${req.params.message} → ${resposta}`);
return resposta === 'sim' ? { action: 'accept', content: { confirmar: true } } : { action: 'decline' };
});
const fim = await cliente.callTool({ name: 'reservar_vaga', arguments: args });
console.log(`resultado: ${fim.content[0].text} · isError=${fim.isError === true}`);
await cliente.close();
await handler.close();
process.exitCode = fim.isError ? 1 : 0;1ª volta: resultType=input_required · pede: confirmar [cliente] pergunta ao usuário: Reservar 1 vaga em "HTML semântico para agentes" para aluno@exemplo.com? → sim resultado: reservado: html-01 para aluno@exemplo.com (restam 2) · isError=false saída: 0
1ª volta: resultType=input_required · pede: confirmar [cliente] pergunta ao usuário: Reservar 1 vaga em "HTML semântico para agentes" para aluno@exemplo.com? → nao resultado: reserva cancelada pelo usuário · isError=true saída: 1
A refusal becomes isError and exit code 1: the seat is still there.
Without capabilities.elicitation, the server has no way to ask for the confirmation.
cd ~/projetos/formacao-webmcp-mcp-v72/kit node teste-sem-capacidade.mjs; echo "saída: $?"
recusado: -32021 Cannot request input 'confirmar' (elicitation/create): the request's client capabilities do not declare the re saída: 1
The message is cut off at 110 characters by the script itself (slice). The SDK refuses with -32021 before sending the request. In a real host, this means that client can't use the tool with confirmation: say so in the description or offer another path.
inputResponses comes from the client. Validate it with a schema (acceptedContent does this) before acting.
The server is stateless: the 2nd round is a separate request. A multi-step flow keeps what has already been proven in requestState, signed with createRequestStateCodec (HMAC). It is signed, not encrypted: no secrets inside.
On a 2025 connection, the server SDK converts the input_required into an old-style elicitation/create (shim on by default). The same handler serves both eras.
The yes, the no and a confirmation of your own.
Run both blocks.
Done when: node teste-confirmacao.mjs nao → reserva cancelada pelo usuário · isError=true and saída: 1; with sim → reservado: html-01 and saída: 0. In both, the 1st line is resultType=input_required.
Run the client without the capability.
Done when: recusado: -32021 and saída: 1.
On your service's tool with consequences (lesson 3), ask for confirmation with inputRequired.elicit and handle the no. Copy teste-confirmacao.mjs, changing the name and arguments.
Done when: your test with nao ends in saída: 1 without changing anything; with sim, in saída: 0.
Question 1 of 4
In the 2026-07-28 revision, how does the server ask the user for confirmation?skill
Question 2 of 4
The user declined. What does the kit's handler do?skill
inputResponse shows an action other than accept; the handler returns isError and the seat is still there.inputResponse shows an action other than accept; the handler returns isError and the seat is still there.Review: The reservar_vaga handlerQuestion 3 of 4
A flow asks for confirmation and then for the scope. Where do you store the fact that the confirmation already happened?
Question 4 of 4
The client did not declare capabilities.elicitation and calls reservar_vaga. Result?
Pick an option. The explanation appears after you try.