LangChain and LlamaIndex

npm i @constaia/sdk @langchain/core @langchain/anthropic zod

import { Constaia, ConstaiaError } from "@constaia/sdk";

const constaia = new Constaia(); // reads CONSTAIA_API_KEY

export const ALLOWED_TYPES = ["es_dni", "es_nie", "passport", "medical_certificate_sport", "payment_receipt"];
const ALLOWED_URL_PREFIXES = ["https://files.example.com/uploads/"];
const KEY_FIELDS = [
  "document_number", "nie_number", "first_name", "last_name", "last_name_1", "last_name_2",
  "birth_date", "expiry_date", "amount", "currency",
];

export const TOOL_DESCRIPTION =
  "Validates a document uploaded by the user (Spanish DNI, NIE, passport, sports medical certificate or " +
  "payment receipt). Returns the verdict valid, invalid or review, the reasons and the key data.";

export async function runValidateDocument({ file_url, expect, checks = {} }) {
  if (!ALLOWED_URL_PREFIXES.some((p) => file_url.startsWith(p))) {
    return { error: "file_url not allowed: only documents uploaded to the application are accepted." };
  }
  if (!expect.length || !expect.every((t) => ALLOWED_TYPES.includes(t))) {
    return { error: `expect may only contain: ${ALLOWED_TYPES.join(", ")}` };
  }
  try {
    const analysis = await constaia.analyze(
      { fileUrl: file_url },
      {
        expect,
        language: "en",
        checks: {
          notExpired: checks.not_expired,
          minAgeYears: checks.min_age_years,
          holder: checks.holder_full_name ? { fullName: checks.holder_full_name } : undefined,
        },
      },
    );
    return {
      analysis_id: analysis.id,
      status: analysis.status,
      verdict: analysis.verdict?.status ?? null,
      reasons: (analysis.verdict?.reasons ?? []).map(({ code, severity, message }) => ({ code, severity, message })),
      fields: Object.fromEntries(
        KEY_FIELDS.filter((n) => analysis.fields?.[n]).map((n) => [n, analysis.fields[n].value]),
      ),
      warnings: analysis.warnings ?? [],
    };
  } catch (error) {
    if (error instanceof ConstaiaError) {
      return { error: `${error.code ?? error.type}: ${error.message}`, request_id: error.requestId };
    }
    throw error;
  }
}

import { tool } from "@langchain/core/tools";
import { HumanMessage, SystemMessage } from "@langchain/core/messages";
import { ChatAnthropic } from "@langchain/anthropic";
import { z } from "zod";
import { TOOL_DESCRIPTION, runValidateDocument } from "./constaia-tool.js";

const validateDocument = tool(async (input) => JSON.stringify(await runValidateDocument(input)), {
  name: "validate_document",
  description: TOOL_DESCRIPTION,
  schema: z.object({
    file_url: z.string().describe("https URL of the document, exactly as the application provides it."),
    expect: z
      .array(z.enum(["es_dni", "es_nie", "passport", "medical_certificate_sport", "payment_receipt"]))
      .min(1)
      .describe("Acceptable document types."),
    checks: z
      .object({
        not_expired: z.boolean().optional(),
        min_age_years: z.number().int().optional(),
        holder_full_name: z.string().optional().describe("Expected full name of the holder."),
      })
      .optional(),
  }),
});

const model = new ChatAnthropic({ model: "claude-sonnet-4-5", maxTokens: 1024 }).bindTools([validateDocument]);

const messages = [
  new SystemMessage(
    "You help review registrations. Use validate_document to check documents. " +
      "If verdict is review or status is not completed, say it is pending review.",
  ),
  new HumanMessage(
    "Is https://files.example.com/uploads/dni_valid.jpg a valid DNI of María García López, who must be an adult?",
  ),
];

for (let turn = 0; turn < 5; turn++) {
  const ai = await model.invoke(messages);
  messages.push(ai);
  if (!ai.tool_calls?.length) {
    console.log(ai.content);
    break;
  }
  for (const call of ai.tool_calls) {
    messages.push(await validateDocument.invoke(call)); // returns a ToolMessage
  }
}