mcp-api-tools

Instructions

Implementation Reference

• src/tools/jwt-decode.ts:42-82 (handler)

  The implementation of the jwt_decode tool handler.

  export function jwtDecode(token: string): JwtDecodeResult {
    const trimmed = token.trim();
    const parts = trimmed.split(".");
  
    if (parts.length < 2 || parts.length > 3) {
      throw new Error(
        `Invalid JWT: expected 2 or 3 parts separated by dots, got ${parts.length}`
      );
    }
  
    let header: Record<string, unknown>;
    let payload: Record<string, unknown>;
  
    try {
      header = JSON.parse(base64UrlDecode(parts[0]));
    } catch {
      throw new Error("Invalid JWT: unable to decode header");
    }
  
    try {
      payload = JSON.parse(base64UrlDecode(parts[1]));
    } catch {
      throw new Error("Invalid JWT: unable to decode payload");
    }
  
    const now = Date.now();
    const exp = typeof payload.exp === "number" ? payload.exp * 1000 : null;
    const isExpired = exp !== null ? now > exp : false;
    const timeUntilExpiry = exp !== null ? formatDuration(exp - now) : null;
  
    return {
      header,
      payload,
      signature_present: parts.length === 3 && parts[2].length > 0,
      issued_at: timestampToIso(payload.iat),
      expires_at: timestampToIso(payload.exp),
      not_before: timestampToIso(payload.nbf),
      is_expired: isExpired,
      time_until_expiry: timeUntilExpiry,
    };
  }

• src/tools/jwt-decode.ts:1-10 (schema)

  The interface defining the structure of the decoded JWT result.

  export interface JwtDecodeResult {
    header: Record<string, unknown>;
    payload: Record<string, unknown>;
    signature_present: boolean;
    issued_at: string | null;
    expires_at: string | null;
    not_before: string | null;
    is_expired: boolean;
    time_until_expiry: string | null;
  }

• src/index.ts:110-124 (registration)

  The MCP tool registration schema for jwt_decode.

  {
    name: "jwt_decode",
    description:
      "Decode a JWT token without verification. Returns header, payload, expiry, issued-at time, and whether the token is expired.",
    inputSchema: {
      type: "object" as const,
      properties: {
        token: {
          type: "string",
          description: "The JWT token string to decode",
        },
      },
      required: ["token"],
    },
  },

• src/index.ts:223-228 (handler)

  The request handler switch case for the jwt_decode tool.

  case "jwt_decode": {
    const result = jwtDecode(args?.token as string);
    return {
      content: [{ type: "text", text: JSON.stringify(result, null, 2) }],
    };
  }